You need to understand that sponsors aren't there looking for you. You need them. That's why FIRSTLY you need to understand why you're looking for sponsors. Reasons can be:
# you want to earn money
# you want to increase your traffic
A) If your channel is weak i.e. less than 1 lakh SUBSCRIBERS, you should really focus on how to make your content better. Because at this stage people LIKE you but not all them are wanting to subscribe you. There can be various reasons:
1. Your video content is not good enough.
2. Your video content is partially entertaining.
3. Not all your videos are enough pleasing and satisfactory.
4. You randomly post video, you don't have schedule.
5. You're copying someone else's content.
6. You are not creating unique or distinct content, it similar to others.
7. You are not focusing much on what your audience want to view.
If You tube is your hobby, continue you work. You'll be recognized one day. And seriously if it's a hobby you won't want sponsors that badly. You can try to make a really good video and pay for it to go on trending list. But if you want to do it make sure you have good content so that you can hold your new audience as subscribers.
If you tube isn't hobby, just doing it because you are seeing others and you want to do it too. It will never work. The chances of you being successful here or not are 98:2.
B) If your channel is progressing and you have 1M+ subscribers and you need sponsors. What you should do is:
1. Work harder and observe demographics.
2. If you have more traffic of teenagers, review products that teenagers use. Mobile, stationery, android games etc.
3. But keep creating because you are growing.
4. Also you can do collaborations. Approach you tubers with similar number of subscribers and meet them and make video about it. It will increase the traffic of audience on both the sides. Consecutively sponsors will notice you if you go on trending.
C) And if you have already few millions subscribers, then you should not worry because it won't be long when you'll find sponsors at your door looking for you.