The official rules for aerial combat can be found here. They are, I warn you, fairly complicated, and can be a real headache to run. I personally hate them.
So much so that I’ve created an abstract flight houserule, which eliminates most of the “3D-ness.” It is admittedly abstract – there are corner cases where this flight rule cannot do things you’d logically expect a flying creature to be capable of – but it’s much easier to run, and makes flight less incredibly powerful.
For the record, flight at 1st level is rare; even flying races tend to start with “glide” or similar until they get enough HD. See the Dragonborn from Races of the Dragon or the Raptoran from Races of the Wild for examples.
The reason for this is that the importance of flight is almost impossible to quantify. In open spaces, flight can make for completely asymmetric situations: that is, cases where the flyer can attack with impunity, because those grounded cannot meaningfully respond. It’s such a big deal that flight is considered by optimizers to be one of the most crucial things for any character to have covered: if you don’t have a class or racial feature that does it, you need to find something else that does (the Feathered Wings graft from Fiend Folio is a great choice if one’s alignment is flexible).
My houserule limits this somewhat as well, by the way.
Best Answer
Not really. Most things work normally, except for the issues that the articles in the other answer mentioned. The primary one of those being that you can't take full round actions if you have a minimum forward speed (aka: average/poor/clumsy maneuverability and do not have Hover). Beyond that, flying is considered movement, so for combat purposes it's treated that way except when the flying rules say its not.
For ranged weapons specifically, altitude differences should also be factored into your range increments. After all, if someone is directly 50' above you, they're not in the same square! (A table here mentions that issue, squares while flying are 5x5x5 cubes.)
Unfortunately, calculating those distances accurately in three dimensions isn't all that simple. If you want an accurate measure, you can use the Pythagorean theorem. That is, if an enemy is 25' away horizontally and 20' above you, the distance is this:
You can imagine how doing that at the table would get tedious pretty fast, but I'm not aware of any rule they came up with to simplify it in three dimensions.
(If you find the flying combat rules overly difficult, KRyan made a set of variant rules that address this and several other complexities of flying which might be of interest.)