Well, since you ask...
You could check the "Inactive users" and look for obvious bots (e.g. "BuyingCialicOnline") and delete them.
Also, decide whether Peeterlink is a bot that managed to activate itself, or a legitimate user. You could send an email from the administrator account to confirm, and if you don't get a satisfactory answer within a set amount of time, then delete it / him / her.
Also, there are inactive users that date from long before the present invasion. Some have never posted, and never been activated (e.g. Raksha from 2005 and Alpha Wolf from 2006). These you can do the same - contact them, and if you don't get a satisfactory answer delete them. Others are inactive because of changing their profile details (e.g. laidensk from 2005, Zimeta08 from 2006). These are more likely to be real people. You may try to contact them to see if they're having any trouble activating themselves.
Well - you did ask for things to do!