Q: How do I speed my iMac up?

Since I installed Mavericks my iMac slowed down significantly. Start-up, shut down and opening of programs is so slow I regret upgrading on a daily basis. But worse than that is iPhoto which is so slow that sometimes I have to take a walk before it is ready. Reminds me of the old Windows-days. My iMac runs Windows 7 on bootcamp for a game and there everything is fast and snappy like my iMac once was under Mountain Lion. I have wiated for the first updates but it hardly helped. Is there anyone with an conclusive idea? I am at the brink of buying a brand new iMac but is it really necessary? We have a 2006-white-iMac around the house which still works perfectly. Admittingly, not under Mavericks. Lucky him.