Q: Can I have more than one trade skill over 200?
A: Yes. You can automatically take one of the general trade skills over 200 skill, up to the hard cap of 300 skill. You then need to use Alternate Advancement points to take any other general trade skills over 200. The general tradeskills are: Baking, Brewing, Tailoring, Smithing, Jewelcraft, Pottery, Fletching.
You can always raise a class-specific or race-specific skill (Poison Making for rogues, Alchemy for shaman, Tinkering for gnomes) to its maximum if you are the right class or race. No AA points are required. Also, taking one of these skills over 200 before a general tradeskill will not prevent you from later taking one general skill over 200 without AAs.
Q: How do I use AAs to go over 200 skill in more than one general trade skill?
A: The AAs you need to purchase are in New Tanaan Crafting Mastery. Each level of this ability costs three points and allows you to raise one additional general tradeskill over 200. New Tanaan is in the first set of AAs that become available, at level 51.
Q: Which skill will New Tannan Crafting Mastery raise? Can I pick?
A: Once you purchase a level of New Tanaan, the next skill that you raise to 201 by skilling up will be the one to use the AAs. So if you have more than one skill at or close to 200 (and one already over), you should wait until you are ready to work on the one you want to raise over 200 before you purchase the AAs. If you are wanting to raise fletching but do some non-trivial tailoring first, be careful not to let tailoring hit 201 before fletching does, or you're stuck with tailoring for that level of New Tanaan.
When you want to take yet another skill over 200, just purchase another level of New Tanaan for another three points and skill it up.
Q: Can I raise skills over 300?
A: Yes. You can now raise your skills up to a maximum of 350 unmodified, but it constrained by level, requires a lot of AA points before you can even start. Once you've reached the appropriate level and have purchased the appropriate AAs, you raise your skills to 301+ by learning different recipes, not by making the same recipes over and over like you did to get from 1 - 300.