Cleaning and speeding up my Mac

I was just wondering how do I speed my computer up and check for repeat files and things that might be slowing it down?

Thanks for your help,

Macnewbie

In a word - OnyX, from here Titanium Software. You don't say which OS you're using, but OnyX covers the field from Jaguar onwards. Use OnyX to repair permissions, run maintenance scripts, remove duplicate files, optimize (update) the system; plus various other functions.