Significant Magic Items (particularly weapons, incl staves/rods) - These items level up with the character. Character level (sometimes total, sometimes class depending on the item) determines what attributes and bonuses the character is able to unlock. So as the character gains levels the item becomes more relevant.
BM/AM (before monster/after monster) Initiative - Monsters/NPCs are given a static initiative. They don't roll. PCs roll each round (d10). If they match or beat the monster's static initiative they go before the monster; if lower they go after. Then the players decide the order of actions for the PCs in their initiative slot. The CHARACTERS don't discuss tactics, but it gives a nod to their cohesion as a group to let the players do so. And since different characters might get grouped together each round it keeps strategies from becoming too static.
I think someone somewhere called this the Rule of Cool - Say yes (or at least "yes, but") to players as often as possible, particularly during chargen. I've always been a sandbox/seat-of-the-pants kinda GM so this is a wee bit easier for me than it might be for more structured GMs, but I'm of the opinion that you can't break the game in every direction at once, so even when a player's idea looks like a blatant avenue for abuse, it can usually be moderated - and can often be entertaining as hell.
That said, I still tend to have multiple bans in place as concerns the flavor of a given campaign.
For instance, I might allow one Gunslinger PC if he is from another plane and willing to take the disadvantages of being a literal stranger in a strange land with issues obtaining ammo. I don't ban Summoners outright, but I can't get the Pokemon image they've always presented to me out of my head.
And there are generally only ever 3 Paladins in my game world at any one time - LG, LN, and LE. Likewise, I prefer only one paladin PC per campaign.
Winged races are forbidden at low levels (but vestigial wings and the like are allowed where appropriate) and aqua dependent races (need to be doused in water daily to survive) and bestial races (those with a whole body or whole head of an animal - centaur, minotaur, etc) - are discouraged.
Some peevy metagamey rules -
No phones/tablets/laptops/novels etc in use at the table. (if you need to make or take a call leave the table - preferably during a regular break, but hey, life happens).
Too many instances of *Oh, is it my turn?* may result in an answer of *no* and a nod to the next guy.