while playing somebody i slam them they bring it back and a rally is started. but i only usually keep it going for about 7 round then i have to chop what should i do to keep on  rallying 

If they loop/drive, IMHO you should do the same to continue rallying. Unless you are a defensive player, you chop their strokes and ensure your returns are on the table.

The strategy that has been used by Chinese players is that finish the point as fast as possible. It is okay to slam the third ball or fifth ball to get the point. But make sure you will get the point. It is a good practice to try some 3 rd and 5 th ball attack yourself and keep that for your game. I have some strategies which I will use only when things go bad.

Although I have said that my services are not that good - I have to get back to practice some tricky serves.

For single play, 50% of the points come from the service. Work on your serve as well as practice on receiving serve.
This will help you in getting the points.

You are exactly right. Your control of the game starts from the serve rather than in a rally. I have many times seen if I can control the game from the serve itself, I can save myself. If I do a loose serve, I'm in trouble.

Well, try not to lose a serve. Even if your serve can be well received by your opponent, there is always the 3rd ball attack in your earlier post. Failing that, there is always the 5th ball attack.

Important thing is practice the serve. The trickier the better.