Learn as much as you can before investing.
If you keep bitcoins diversify the amount of coins between different wallets.
First thing you need to thing about is if you will use the qt-client or an online wallet on a website.
If you keep your bitcoins in an online site wallet you are transferring trust onto the adminstrator of that website.
There were sites hacked that lost all the coins.
Luckily there is a lot of information on this website about securing your wallet.
I personally also learned a lot from this wiki:
https://en.bitcoin.it/wiki/Main_PageIk mis Check Point