This is a great game but it can be very hard, especially as you near the end.
Here's a few tips that might help.
Always match as close to the bottom as you can. That way you are more likely to get spontaneous matches as tiles fall in from the top.
Fill your bonuses as fast as you can. Then use them.
Try to only use those bonuses you can refill on that level. If you can refill the hammer, use the hammer.
When you get to where you only have one more match to make to finish off a level, check your bonuses before you do it. If you have time, fill any bonuses you can. Use an area of the board away from the tiles you need to finish the level so you won't mess yourself up. This way fresh bonuses will be there for future levels.
Get rid of chains and other blockages as quickly as possible. Using bonuses may be the only way for some levels but usually once you've cracked one or two chains open, things get easier.
Play as fast as you can. If you can finish the earlier levels without losing any lives, you'll have more left for when the game gets harder.
One other thing. My DH felt that it was easier to tell certain tiles apart in Cradle of Persia. That wasn't really the case for me but you should demo COP to see if it makes a difference to you. It did for him. He was never able to complete COR but did COP just fine.
Other than that, it's about persistence. Trust me. You can finish this game. I've done it more than once and so have lots of other people.
Keep at it. You'll get there!