I wonder if you could perhaps offer some advice ... about dealing with combat without minis and squared-off maps. For someone who's been "in the game", if only barely, for as long as I have, I've GMed very little and I hate managing exacting maps, measures, and minis, but I'm just not confident enough to generalize that stuff and feel like I'm being "fair" to the players. So I always feel like my options are jumping out of a plane without a parachute or spend so much time on mediocre combat maps that I've got no energy for making up FUN stuff for the players to do.This is an interesting topic to me, as I play quite a few games that have rules for tactical displays yet I don't use one most of the time. And lately I've been musing over giving 3e a second try, but I'm not sure I want to break out the battlemats and figures to do so. Here are my thoughts, perhaps others will chime in.
Advise players that you don't use a tactical display.
Communication with players is always important, especially regarding your house rules. In games with point builds or feat-picking some folks will get sore if they think they lacked crucial info about how you run your game. That being said, don't actively discourage them from buying or picking anything but the most tactically intensive options, because...
Your players' choices tell you what is important to them, respect that.
Let's say that one of your players in a new 3.x game takes Combat Reflexes, a feat designed to give you extra Attacks of Opportunity, despite knowing that you don't use a combat grid. You need to make sure that there are opportunities for this PC to use that feat. A mass of suicide bomber kobolds try bum rush past the front line to blow up the mages? A great time to use some Combat Reflexes to stop those little mofos. In general, you should lean towards allowing these tricks rather than forbidding them. If a player asks "Can I take a 5 foot step and full attack?" your default answer should be yes. Sometimes you'll have a perfectly good reason why they can't use their tactical advantages, but I feel like you should give the PCs the benefit of the doubt when the situation is ambiguous. Or at least allow a die roll. (E.g. "Roll d10. That's how far you are from the foe in feet.") After all, you can always add a few more bad guys to the adventure to offset this advantage.
Develop some rules of thumb for area affect attacks
In my games flaming oil will hit d4 foes in most situations. Last session one of the werewolves was smack dab in the midst of the party (it tore through the door-opener and leaped into the room) while its two were-buddies followed in more slowly. The next round I ruled that no single Molotov could hit all three without endangering the party, so the oil-lobber targeted just the other two. On the other hand, one well-placed flask has ignited an entire pack of giant rats.
Using the principle outlined above, I generally assume that fireball or lightning bolt is going to be able to target a crapload of foes. I actually map out these particular attacks on my dungeon maps (I use the 33 10' cubes rule for fireballs, which is fun on a bun), but you can just as easily make up things like "This is a big room, but there are a LOT of ghouls in here. Roll 1d6 for the number of ghouls not caught in the blast." Or you can just pencil in your rulebook "Fireballs affect 2d6+6 targets."
Don't sweat it if things get crazy
Let go of the idea that your brain has to perfectly emulate the rules as written for the tactical display. Once you give up on that impossibility you can start to have fun doing this. Instead of asking yourself "How should the tactical rules apply here?" consider some alternative questions like "What makes most sense in this situation?" or "What would be the funnest or stupidest thing to happen?" And do your best not to look up fiddly little rules in play. A snap decision like "You have a 4 in 6 chance of pushing the orc jester into the scorpion pit" trumps even 30 seconds spent looking up the pushing rules.
Enforcing the written rules is a small part of being a good DM. In my experience the players will respect that you want to keep the game moving as long as they are convinced you are not an adversarial DM. I can smile while giving my players all sorts of bad news. And they don't blink when I run roughshod over their notions of how D&D works. How can I get away with this? Because they trust that I'm there to have a good time with them, not against them. Show that you will call things done the middle, but will give them every chance when you're in a grey area. Let them use and abuse the tricks on their character sheets and the crazy plans they come up with. Then when you kill them they'll understand that it wasn't anything personal.