You've asked us an impossible question to answer ;-)
I can give you a few tips, but you are going to have to test things for yourself to see what performs. There is no "one size fits all" for AdWords.
The key is relevancy. If someone is searching for a particular product or product category, show them an ad that is relevant to their search.
If we use boys bikes as an example, you wouldn't want to show them a generic ad covering girls and boys bikes. It would more suitable if the ads mentioned boys bikes. Same again for "boys mountain bikes", show them a boys mountain bike ad. See where this is going?
The closer you can get to the users query, the more likely it will perform better.
Maybe try dynamic keyword insertion in an ad or 2. This will insert the keyword into the ad copy which can help increase CTR's.
Take advantage of the ad extensions. Sitelinks can really help increase CTR as well as get additional information into the ads. You have a few options for extra extensions. (if you are going to use enchanced campaigns, you can set AdGroup level sitelinks which could help in an ecommerce campaign)
Just make sure to be running at least 2 ads per AdGroup so you can test and measure the performance against each other.
There are so many things you could be testing. Capitalisation, prices in ads, calls to action, display url, landing page etc. The list goes on and on and on.
There are some great ideas from the Community there! I hope they help.
This link here might also help if you would like to read a little bit more on ad quality.
In terms of writing good ad copy, it can help with your quality score to try and include some of your keywords in your ad text, when it is relevant.
Hope these ideas help!
Imagine having to have an email fight with Adwords Support over a clients physical office address that has been on maps for 4 years. Because they (India) dont understand that it is the office address, not the postal address (which is a PO Box) the site has been suspended for nearly 3 weeks. Called, emailed, amended, explained, did pictures, and absolutely no use!
Any suggestions Purefuzz ?