instead of completely random, it should know not to display tasks that you've already voted on, or within the first couple pages of any filter. Old tasks that have been forgotten, and tasks with the least number of votes should be more likely to come up.

You could come up with a better weighting scheme than just "lowest voted". Something involving a combination of everything you mentioned, and other considerations.

Already been accepted:),just not completed:(

and make it so you randomize the catagories not all the tasks at once.