Ensuring GM variety is vital in any homebrew game. It's important to mix up what you are doing, and to send the PCs through a wide variety of challenges.
1: Players will get bored if they are tasked with the same type of objective over and over. If every social challenge can be solved by diplomacy, if every enemy in a dungeon is undead, if every NPC is a fighter or wizard, then players will fall into a rut very quickly.
2: Every player should be given a chance to shine. If you have a cleric who is built around defeating the undead, you must make sure that undead pop up in your campaign. If a Bard's Knowledge (Nobility) never gets used, then he will regret ever taking it. If a ninja has a fantastic Reflex Save, then he will get annoyed if a fireball never comes his way. Each PC has his own unique abilities, and these must be utilized to ensure the player enjoys the game.
3: Characters should be faced with challenges that they are not specialized in. This will force them to think creatively, and will add to the realism of the challenges. None of your characters have area attacks? Send a swarm their way. Nobody has good swim? They've got to think of another way to flip the underwater switch.
The best way to ensure GM variety is to keep track of what you've used each session. You'll notice trends, and after a few sessions you may realize that you haven't placed a single trap for the rogue to disarm. Or, you may realize that the PCs are finding combat easy because they specialize in crowd control, and you have yet to send them a solo.
Here is a fancy spreadsheet that you can use to track what you use when you use it. Save it to your own Google Drive to make edits. If you use something in a session, whether it be a skill check, a type of monster, or a save, place a "1" in the appropriate box. Your totals for each skill/save/enemy will show up on the left. Try to get rid of those zeroes, and make sure that every dire wolf has his day!