What kind of presets? OS and Version of AE down to the last decimal point please...
IF you are looking to install animation presets the easiest way is to create an animation preset of your own and then click save and look at the path AE chooses. Personally I put all of my AE animation presets in a folder I have created in Dropbox so I have them available on all my machines. I then put an alias to the dropbox folder in the normal location Here's the structure on a Mac:

If you are not dealing with Animation preset please let us know. To use a preset you don't have to put them anywhere special, you just have to browse to their location using the Animation menu. To get them to show up in the Effects and Presets Panel you should use the standard user presets directory. It's not a very good idea to start mixing them with the standard presets that come with AE.