Advice on balancing encounters around a party with differing levels?

I'm in a tabletop community that runs a series of loosely related one-shots, characters start at level 5 and level up after every session to a maximum of level 10. I will hopefully be acting as one of the DMs soon and want some tips on balancing encounters for a party that can vary from level 5 - 10. Typically parties will be from 4 - 5 players.