Are you sure you want to do solo mining ? I'd rather do Pool mining if I were you

But, here is the how to : you can use Yenten-qt.
- Start your wallet, then go to Help » Debug Console Type setgenerate true, and you're mining solo
You can also specify the number of threads to use: let's suppose you want to dedicate three threads for mining, you can type setgenerate true 3

- To stop mining, type setgenerate false

- To retrieve informations about the current mining process, type getmininginfo

Good luck