Now that you have installed or are using Salesforce.com, SugarCRM or vTiger, all you have is a glorified address book. Before you start adding users you need to set up the crm so it works for your business.
Start with roles definition. Things like support person, marketing person and sales person. Then the management. Basically build out a ORD chart. For each position figure out what they need access to, and what rights. For instance a support person needs access to all accounts, but have read only (view) rights. Not the ability to delete them.
I find it useful to have each level only able to view their items and those below them. For instance a sales person should only be able to view their accounts. A sales manager should be able to view all accounts below them. It gets trickier when you have inside sales and outside sales. I tend to put inside sales above outside sales typically because they support mutliple sales people.
And for those documents, accounts or whatever you want available to everyone, just create a level at the very bottom. I tend to call the role documents or something like that.