How I Mod?

Can someone please tell me how i make a mod, i know a lot about computers and i'm sure i could manage it i just need a starting point though, thank you!

It would be good if you could send me some links for some sites as well. I did try one mod making tool that i got off the tools section on the Minecraft forums but they're never any helps, but if you know any decent tools that make modding a little bit easier then that would be great, hope you can help!

JOSHREADING....