I'm actually stuck brewing 1 gallon batches for awhile since I'm redoing my backyard. I've brewed about 15 this year and they have mostly been experiments. There was some good advice above but here's some more:
1. Get a refractometer. Wort is precious when brewing 1 gallon batches so putting some into a hydrometer jar is like giving away gold. Check your preboil gravity and make adjustments if needed. I usually boil a few longer. I've gained .005 gravity in less than 10 minutes of extra boil.
2. Calculate your boil off accurately. Boil off with 1 gallon batches makes a huge difference in your OG. I lose about .5 gallon for 60 minutes.
3. Calibrate your pot volume. This is less important if you have really know your boil off rate.
4. Brew 1.25 gallon batches if you're going to have a bunch of trub. Lots of hops and certain grains cause create tons of trub. I brewed two batches a couple days ago (old ale and gruit) and one had tons of trub the other barely any. If you suck up a ton in your siphon I usually fill my gallon jug to the top and put in the fridge overnight. The next day rack off a gallon of clean wort into a new jug.
5. Skip the whirlfloc tablet. I've tried these a couple times in my 1 gallon batches and it creates to much break material. Maybe others have had bad luck.
6. Have a scale that weigh hops by the gram since you'll be using small amounts.
7. If you don't keg carb these (2 liter soda bottles) a good thing to use for bottling is the 1/2 tsp sugar cubes. I bottle straight from the fermenter with a bottling cane and mini autosiphon. I don't dissolve the sugar but I shake it up after capping.
Good luck and have fun! I love these small batches. I've been documenting some of my brews at http://brew52.blogspot.com