If you've never used it before, try your best to get and use a voucher, so you can get a feel for it without losing too much money. Adwords is really easy to lose money with if you don't know what you're doing.
use limited good keywords and configure manually CPC , Choose perfect add location , not whole world target specific location and then enjoy the benifit
Use keyword tool of Gooole adwords for choosing the best buyer keywords.Just type one phrase and Google will suggest you a list of keywords with the competetion for that particular keyword,local searches and global searches for that keyword and much more.Its the best keyword research tool i have ever found.Would help you a lot.
refer Google beginners guide it will really helpful for you to understand basic steps: http://adwords.google.com/support/aw/bin/static.py?hl=en&page=guide.cs&guide=21899
target keywords you are not ranking good for. If you rank on the top for a keyword don't use it in Adwords. Also look for keywords that are not really that competitive at first or you will exhaust your budget quickly. Use this tool: https://adwords.google.com/select/KeywordToolExternal
Lots of good advice above especially starting with very cheap keywords untill you get the hang of it.
Be careful with adwords and choose your budget wisely. Adwords is just about trial and error. If one campaign is profitable for you you can increase your daily budget.