How to improve system performance byclean up activities

I am working on Windows 8 system and facing lot of issues with my system performance. I have tried a lot of time to use cleanup activities to tackle this, but unable to solve this issue. I have searched on internet that there are many services that get loaded while system start up and which are actually not used on daily basis. I think that these services are my basic problem. Can somebody guide me on which services should I permanently delete?
