First, relax, you have plenty of time to figure it out, try it, and test it.
Read my suggestions. Wait for others to give their advice too before doing anything, as it turns out I am fallible. If you are really paraniod, after deleting evidence of visiting "bad" sites, only visit lots of "good" sites to generate a "good" history.
I think the main thing is to delete the History, Caches and Cookies on your browsers. I never remember how to do it, I just hunt around until I find History, Caches and Cookies. Basically, just look for the Preferences or Internet Options page in your web browser and clear the History and the Cache and Cookies. If you delete all Cookies, sites like Amazon won't automatically know it's you until you log in and it creates another cookie. Other sites may not automatically remember things like your login name, you may have to type them in again when you revisit those web sites.
Oh, this is a little harder to find than I remembered, had to hunt a bit.
This may vary depending on your browser version and operating system version. Would have been faster to just ask you what computer/browser you have first, oh well.
On a WINDOWS computer,
For InternetExplorer:
Use the menu Tools/Internet Options and click Clear History, also, on same page, Delete Temporary Files and Cookies.
For Netscape:
Use menu Edit/Preferences
On left, click Navigator triangle to see list, click History in list, click Clear History, click Clear Location Bar.
Scroll down on left to see Advanced, click triangle to see list, click Cache
click Clear Cache.
Scroll down on left to see Privacy & Security, click triangle to see list, click Cookies, on right, click Manage Stored Cookies, delete cookies you don't want or delete all.
On a MACINTOSH computer,
For InternetExplorer: menu Internet Explorer/Preferences window
Click Web Browser triangle to see list, click Advanced in list.
Click Clear History and Empty Now under Cache.
Scroll down on left click on Receiving Files triangle for list, click Cookies, click on cookies you don't want and delete.
For Netscape: menu Netscape/Preferences.
On left, click Navigator triangle to see list, click History in list, click Clear History, click Clear Location Bar.
Scroll down on left to see Advanced, click triangle to see list, click Cache
click Clear Cache.
Scroll down on left to see Privacy & Security, click triangle to see list, click Cookies, on right, click Cookie Manager, delete cookies you don't want or delete all.