First, and most importantly, know your local laws. Don't play for cash if it's not legal. Nothing can end a night on a sour note quite like facing criminal charges.
Determine how many players you're going to have over. This sets the parameters for everything else that you need to decide. I've played with 6 to 14 in home games, and all of those numbers work fine -- but they require different setups.
Decide how many tables you're going to use. For up to 10 players, I recommend a single table (if you have one large enough). For 11 to 16 players, I recommend two tables. For 17 to 24 players, I recommend three tables. Beyond that, you're on your own.
Have plenty of drinks and snack food, making sure the snacks you serve aren't likely to leave residue. In fact, someplayers like to establish a ground rule that no food can be eaten at the playing tables, and that all drinks must be set somewhere other than on the playing tables (e.g. a nearby end table).
Have plenty of poker chips. Clay or clay composite chips, weighing 7.5 grams to 13.5 grams each, are terrific but do cost much more than lightweight plastic chips. If you shop around, you can get 500 good quality chips for less than $100. (Here are some tips on buying Poker chips.)
No matter what kind of chips you use, make sure you have enough. I recommend a minimum of 35 chips per player. 50 to 100 chips per player is even better.
Use brand-new decks of cards. You only need one or two decks per table, they're inexpensive, and there's something really cool about cracking open a fresh deck when you start playing.
Determine your chip denominations. A typical casino standard is $1 for white, $5 for red, $10 for blue, $25 for green and $100 for black. (Note that chip denominations don't necessarily have to relate to the cash involved, if you are playing for money.) But if your group is going to include some less experienced or even novice players, you may want to consider working with only two -- or even just one -- denomination.
In our first game, we decided that every chip was worth $1, no matter the color. In our second game, we used $1 (white) and $2 (every other color) denominations. Both worked very well for our groups, which both had a mix of player experience. (We have since gone to more standard chip denominations.)
Have "dealer buttons" available, one per table. You can buy actual dealer buttons, or just use something distinctive. These are used to keep track of the "dealer" -- which is important even if you use a single dealer at each table (see the rules of Texas Hold 'Em for more information).
Make sure everyone knows the rules ahead of time. If they don't, or even if they do but you have some novices, run through at least two hands so they can get the feel of the game. It's much different from many other forms of Poker.
Consider using two decks per table. While one is in use, someone can shuffle the second deck (to be used for the next hand) to keep the game moving faster.
Increase the blinds. We generally start with blinds at 1 and 2 (or 5 and 10, depending on the denominations of the chips we're using) and move them up every 15 minutes. How fast you increase the blinds, and by how much, is determined by how long you want to play and the value of the chips you're using. For a longer game or with smaller chip values, increase the blinds less aggressively. For a shorter game or with larger chip values, be more aggressive in increasing the blinds.
I recommend that two people be given complete authority to increase the blinds, as long as they both agree. (It's best to have a pre-determined schedule for increasing the blinds, but even the best-laid plans might need some adjustment.)
If you're playing with more than one table, work out a system that allows the players who are eliminated early to continue playing if they want to. When we had two tables, we started with five players at each (a total of 10 players). The first five players eliminated then started a new table (affectionately termed "The Losers Table"), while the five players who still had chips all congregated around the other table ("The Winners Table").
Even if you play for money, you don't want people to leave feeling like they had a bad time. So I recommend keeping the buy-in relatively low -- e.g. the same amount of money you might spend going out to dinner and a movie. Doing so will greatly reduces the possibility of anyone taking the game too seriously, which would cut into everyone's ability to have a good time.
My goals for a game night, with Texas Hold 'Em or any other game, are always the same: have fun, spend time with good friends, and make sure everyone's eager to come back to the next game night.