1st things 1st...know your upcoming spells...get a spell list.
Find a list online, ask people in-game, whatever, just know what's on the docket for your toon. Many of my spells I picked up before I could use them. Someone /ooc'd in a zone and I got an Adept1 for the same price that the ap3 was listed for with the broker. Also, buy from the broker in the tradeskills instance in your beginning zone (i.e. Longshadow Alley), apparently they don't charge you a broker's fee if you've entered the marketplace yourself (i.e. you've purchased a bulletin board to sell in your apt). I've not paid attention to the prices/difference, that's just what I've been told.
Spell upgrades are important, but don't get screwed in the process. I see fools listing some spells for ridiculous prices. Educating yourself a bit will save you quite a bit of money. Also, some spells, it seems, are very rare, even the ap3's, so as a general rule if the spell isn't listed at all in the broker, go buy the ap2. Many of the ap2 spells are 1sp. Some are significantly more like 16sp and that may be an indication that the upgrades for that spell are going to be hard to come by, but I can't, as of yet, verify that for you.
Syph - Mistmoore