If you want to create a custom "default view" for your friends page, create a friends group called "Default View". You can add any friends that you want to it, and this will allow you to view only those specific friends when you go to your default friends page (http://www.insanejournal.com/users/exampleusername/friends/, replacing "exampleusername" with your username). This is particularly useful if you don't want to view specific friends when you go to your default friends page.
Both of these features will only work for you, and only if you are logged in, unless you specifically mark your group(s) as "public". If they are marked as "private" (the default setting), anyone else who goes to any of your group pages will see all of your friends.
Go to the Edit Friend Groups page (http://www.insanejournal.com/friends/editgroups.bml). If you don't remember the address of that page, an easy way to get there is to click the 3 dots after "Friends" on the blue sidebar; then you'll see a link at the bottom of the page saying "If you want to edit your friends groups, go here."
USING A DOWNLOADED CLIENT:
Many clients available for download include the ability to edit or create custom friends groups. For more information on your preferred client, consult its documentation or its menu options. See http://www.livejournal.com/support/faqbrowse.bml?faqid=158 for information on downloading a client. (Note: Not all LiveJournal clients are supported by InsaneJournal).
If you want to delete a group and make a new group, do NOT simply rename one group to something else and change the people that are in the group. If you do, all the people in the new group can see all your old entries you made for people in the old group.
If you delete a custom group, any entries made to that group will still have the "custom" security set, but it won't be set to any particular group. The effect of this is that no one but you has permissions to view these entries; even though they are not marked private, they are effectively private. Additionally, if you recreate the group with the same name, the entries will not automatically be set to that group again. If you would like to change the security level of the entry or set it to a new custom group, you'll have to go back and edit the entry (http://www.insanejournal.com/support/faqbrowse.bml?faqid=2).