You are not alone in this regard. Many of us are 'Aarambha Shoora"s. That is we start something with great interest and even trumpet about it to the whole world. But very soon we get bored of it or just feel uninterested in it and leave that giving some lame excuses.
Only those who overcome the lethargy and excuses and carry on with the action will succeed. Such people are 'Kaam ka aadmi' or real doers.
You also can be easily a 'real doer' and not an 'aarambha shoora'.
1. Enter into matters which can be easily accomplished and which do not need much preparation.
2. Even if not perfect initially start that programme or work or exercise.
3. Slow and steady wins the race. Be slow, but be steady; gradually increase efforts, time, distance or other parameters. For example if you start morning walk, then first day just walk for a short distance and return. Make it that way for a few days. Then increase the distance or speed slowly.
4. Do not get discouraged by any negative feeling. When starting exercise or workout, there may be some fatigue initially. But let that not deter you. Slowly the body gets over the fatigue. Similarly reading a book may invite sleep at first. Do not worry, take a nap. Get up after that and again try to read a few more pages.
5.Consistency is the need. As far as possible be consistent. Do not make unnecessary breaks and stops. That will be retrograde and will defeat all the good efforts.
6.Declare what you do to someone who can criticise and guide you. Let it be your best critic or adversary. They will provoke and even chide you if you fail on the matter. That will make you take it as a challenge.
7.Keep a chart or table about your goals and actual achievements at a pace where all in the family( and even visitors) can see. That will serve as a review and reminder and prod you to go ahead.
8. Keep realistic targets. Divide long term goals to achievable short term goals first. Each achievement will encourage to progress further.
9. Never be afraid of failure. On any downslide review what has gone wrong and take corrections and renew efforts.
10. Join the relevant internet forums where you have people having similar goals. ( For Example ''Indusladies.com" has forum where people keep a goal of reducing a certain amount of weight in certain number of days. There is a countdown chart and achievement at every threshold point.)
Last but not least, tell yourself sincerely and seriously: "I can do it, I will do it'. You can! I bet.