First of all, google your key words and see what your competition is doing, get an idea from that.. Also, experiment with some versions of your ads, and see which ones get higher CTR
You should find the right keywords, write titles and description with your keywords. Don't forget about titles and description sizes.
The best way will be to always track your results and in time you will get the right combination to optimize your ROI.
I think your should be related to your landing page. Whatever product or service you are providing, your ads must able to justify it. Which will automatically going to increase the ROI.
Too long to explain here but that's why I've got a free ebook called Adwords FAQ which covers the basics of what QS is all about. Now, if you want to know about how to make ads more effective, I've got a whole different book on this. There are others of course, you may even find some at your local book store.
Do some research on your keywords... I can't actually tell you what to do, I don't know your niche but I can tell you what not to do. Don't bid too high, being the first it's not always the best. Think about a regular customer behavior, they will check several options before they make a decision Don't lie in your ad, the customer will leave your site as fast as he realizes that the ad was fake.You don't need to lie, I am sure that you have some strengths, let's say: Payment options, Shipping, discounts, quality, etc Don't use words such as "FREE" "CHEAP" they will just generate clicks out of curiosity and you will be paying for those. Use instead "DISCOUNTED" or " 20% OFF" Don't use negative connotations such as "MONEY BACK GUARANTEE" "100% RELIABLE"... customers notice that you are trying to cover yourself. Hope it helps!