Meditation works. It's one of the most amazing experiences in this life.

If you DON'T do them, the definitely won't help. If you sit for a half an hour and tell yourself you have a bad headache, you will most likely give yourself one. Just being able to sit still and quiet your body
and mind for a few minutes is a step in a positive direction.

Positive thinking is better than negative. What you expect ,tends to be realize. I do not think that always working that way,but still it is better than negativism.
As for mediation is good make people to relax

If it is good enough for Al Franken, it is good enough for me, because "I'm good enough, smart enough, and doggonnit, people like me!" (SNL reference). But seriously, meditation can give us a chance to think carefully about our assumptions, and affirmations can challenge the negative assumptions. But we have to be thoughtful about it or it loses any signifigance.

I believe in positive thinking so yes.

I guess it depends on what you expect to get from them.

Meditation works in that it relaxes and relieves stress, which may or may not make it easier to think clearly. The relaxation and stress relief will lead to better mental and physical health. Personally, I find it boring.

Affirmations work in the sense that if done right they can correct negoti8ve thinking patterns, which may ultimately lead to more happiness and success. However simply repeating affirmations at the beginning and end of each day will most likely have no effect. For the vast majority of people you have to vigilantly monitor your thoughts and when you have negative thoughts and make corrections to change your thinking habits and patterns. Most people don't have the patience or cannot get enough of an idea of how do do this correctly through just reading a book.

There are no simple solutions and making lif echanges happens slowly with lots of little changes over time. If you want ot change your life, it is better to just identify one or at most two things to change and work on those, and once you change that one, work on the next one and so on. In my experience, that is the best way to make log lasting changes in you life.