What to study to get successful in career for humanities Student

Since you are a student of Arts and have not written about your weakness in Maths or not. Anyway, you want to get a job, so in my opinion, you can study the following courses:-

There is no need to prepare for civil service you;

A good rank in the cat, mat exam is important for doing an MBA from a reputed university, so prepare well for cat, mat and get admitted to a reputed institute with specialization in HR/ Personnel Management in regular course.
Or Post Graduate Diploma two years full-time regular course in this fields:-PG Diploma in Personnel Management &Industrial relation, HRM, Labour welfare, etc.
But from a reputed university, of course, to get a good job as you desired.

I was good in maths in class 10 i got 89/100 in my boards but currently I have forgotten the concepts of maths

The following are the options for you.
1. Apply for bank clerk or officer jobs. Prepare well for getting selected in the written test and oral examination. You will have a good future if you are getting selected for the same.
2. Prepare well for CAT and try to get an MBA seat in a reputed institute. That will give you a very good scope for excelling in your career.
3. Simultaneously while preparing for CAT, you can apply for UPSC also and you can try your luck.
4. After completing your BA go for B Ed. Once you complete your B Ed, you will have plenty of chances to get a teaching job in a government.
5. You can go for MA in the same subject as your BA. Once you complete your PG, you will be eligible for a lecturer post in any government college or private college.
6. There are many private companies where you can get a suitable posting. You have to look for the advertisement and apply.

Today the job situation in our country is very tight and jobs are much less than that of the contenders for it. So there is a tough competition everywhere whether it is a small job or a mediocre job or a big job.
In this situation what is required is hard work and concentration in one's study and get good score not only in the normal college or school exams but also in the competitive exams. It is to be understood that there is no substitute of hard work in our lives. Whether it is assistant grade or bank clerk exam all the most coveted UPSC IAS exam, same students are appearing everywhere and only the top few get selected.
In most of the exams there are questions based on basic maths, statistics, logical reasoning, English proficiency, general knowledge, and the main elected subjects and lacking proficiency in any one of them could be disastrous for the candidate.
It does not matter whether you are studying arts or science or commerce but what matters is how you are doing in that.
So apart from hard work one has to understand the unemployment condition in our country and should not shy away from any position where one gets selected. There are many departments like Railways, Post Office, State Govt subordinate services, PSUs etc where all types of posts ranging from assistants to officers are advertised and one has to concentrate in them by going through the model question papers which are based on the real question papers of the past in these organisations. Studying and solving the questions helps in preparing for the exam.
There are many career lines today like teaching for which B.Ed. can be done, industrial positions for which BBA or MBA is a must, research work after PG, self employment opportunities etc and one has to focus in one of them wholeheartedly. Getting the job is not the end of a career. One has to acquire learnings continuously to survive in the fast changing business environment today. So considering all these aspects one has to move ahead competing with others in a sustained manner.

In the current market scenario, you might have felt how difficult it is to get a job especially when the youths having their postgraduate degrees with the impressive scores don't hesitate to turn for the interviews of peons or for the similar sorts of jobs. It means that the young generations are keeping their eyes in all sorts of jobs where they could be placed with their little efforts. Hence you need to gear up yourself for trying different jobs though your prime objective is to get selected in UPSC.
I would suggest you the following ways to exploit your job opportunities-
1) While trying for your UPSC examination, you need to think over your B.Ed degree and that too, through the correspondence course so that your precious time is saved for your UPSC. Choose your papers wisely for B.Ed while undertaking the course. You might get yourself enrolled in anyone of the open universities such as IGNOU, Karnataka Open University, Utkal University etc. you might take up the help of some professional institutes to learn more tricks how time can be curtailed in the process of preparation.
2) Since you have had interest in Mathematics at your class ten stage, the same can be revived and try for CAT. You need to clear up the portion from general knowledge, Reading comprehension, strengthening your vocabularies, cracking basic Mathematics up to Intermediate stage. The subject are not difficult to that extent if you are preparing from some reputed institution. You have to be cautious while ticking the correct answers from the four alternatives for each question since this pattern follows negative markings if you are not prudent enough to select the right responses.
3) You might try for Banking Completion of the different banks. Go through the pattern of the questions asked for the last five years so as to establish your opinions of the patterns of the examination. Take the help of your seniors while preparing for this examination.
4) Try your best to secure at least 60 % marks in your graduation so that you could appear for the test of Management Trainee ( Administration) for SAIL, CIL, ONGC etc. You need to clear both written and their oral tests so as be inducted for the posts.
5) Preparation for the state civil service for BDO and other allied services- You may utilise your knowledge skills taught in graduation with the subjects taken up in the graduation level keeping already taught papers as the optional ones and this preparation would be relatively easy if you are consistent with practices. Go through the set of the question papers for at least six years so as to establish the idea of the questions set for these examinations.
However you need to take up your decision relating to your career and should proceed ahead with your firm determination for which you have intense passion for persuading your service goal. Opportunities are immense in other fields as well such LIC, Post - offices, Railways etc but you need to think of seriously in your chosen goal.

It is normal to have doubts about a career after graduation and which path to choose, but as you have already narrowed your options to two it is a good start. As you already know your priorities and what you seek, you have made it pretty clear about a high-paying job and at an early age.
When it comes to starting preparation for a competitive exam, most students want to achieve everything as soon as possible but as we know from the statistics on unemployment in our country that it is not an easy task to get employed at an early age but this is not something to get disheartened. So let us analyse both cases.
As you said you need a high-paying job at an early age, in this case, the CAT exam better suits you as it will provide you with better job opportunities but since it is among one of the exams which are considered very difficult to crack by students it requires an immense amount of hard work and commands over concept, especially your reasoning, mathematical and language domain needs to be stronger.
On the other hand, Civil services which is a very respectable and well-paying option have a very vast syllabus and a lot of content to be studied but it can be studied and covered with a correct strategy, time schedule and disciplined lifestyle since you are from a humanities background and with a good score you have an advantage in this field with a certain amount of background knowledge of the subjects that are important as per the UPSC syllabus.
Now you have to decide in which area you can do better studies with well time management, and what is your inner calling is it just High paying job? or do you want to do something for society while working with a little less amount but a lot more respect and stature?
Since no one can advise you and suggest what is best for you without knowing your calling and the area of interest you lean towards whether it is the private sector or the public, you have to find on your own. So do look at the syllabus of both the exams, watch interviews of people serving in both areas and talk to anyone you know who has worked in these fields and you will get better guidance and motivation for what career option to opt for.

For humanities student, It is necessary to be careful regarding career. Because, humanities student have less career scope compare to science student. But, if you are hardworking then there is no dearth of job opportunities. I would suggest you that at first see your interest area and then try to that field. Since you are humanities student so you can try for UPSC exam and state public service Commission. This is special area where you can try seeing your capability and hard working nature as It is very competitive exam. Apart from it, you can go for teaching job. You do B. Ed after BA and apply for PGT and TGT. Another option is, you can apply for UGC - NET. When you qualify this exam you would be eligible for lecturer job in government college. Besides, you can try for banking, railway where a lot of job opportunities available. You might try for MBA also where you will get job in different company with good salary. Nowadays, many people are doing self business and earning very well.