Hm. Did you try resetting Safari because that particular application is running slow, or was it your approach to helping the whole Mac (that's running slow) run faster? Many things can cause your Mac to run slow, maybe you can explain the symptoms a little more?
Things to check:
1.) Does your system volume (the harddrive) have enough space left? If the empty space on the system volume gets below a certain point, the system has trouble with memory. This might start at 5 GB space left or even 10 GB space left depending on the specs of your machine and depending on what you're doing with the machine at the time of the problem.
2.) Do you have enough RAM for the tasks you want your Mac to do simultaneously? You can check with Activity Monitor (use Spotlight to find this app or open it from /Applications/Utilities). The memory tab should show you a bit of "green" in the graphical representation of memory. For example: My MacBook Air with 2 GB of memory usually has more than 1 GB free space when only running Safari. About 500 MB are reserved (i.e. red).
More generally: What machine are you using, how much memory (RAM) does it have, how much free disk space and what system version are you running?