I've lurked on this site for some time now, but never felt like I had anything worthwhile to say until now. I've found a really great, easy, fast leveling tip involving HQ items and levequests.
The first thing to note is that, whenever you do a tradecraft leve, if you turn in an HQ version of the item, you get a 200% bonus to exp! Awesome! But there's a way you can really take advantage of this.
Part two to the magic is that some leves, after you turn in the item, ask if you want to extend the contract (it will ask this only a few times), meaning you can turn more items in if you have them.
There are several leves this can be used with, but I will use Don't Forget to Take Your Meds as an example. I used this leve to level from 20 to 25 in about an hour. It's great because the item you need is pretty easy to make and HQ's come often enough (with enough luck and skill) that you are more likely to make money than lose it. This leve can be obtained from the levemete in Ul'dah (Eustace in The Quicksand). The leve asks for 5 Intelligence potions, to be delivered to Roarich who is basically right next door (and the Alchemist's guild is in the same city, making it convenient).
So, if you make 15 HQ Intelligence potions, grab the leve, turn in the first 5 (for a 200% bonus - in my case, it was over 14k exp!). Then, he'll ask if you want to extend the contract. Do it! More exp! And again! This is probably at least a full level, or a level and a half on a single leve!
Maybe this is old news to the rest of you, but I thought it was awesome! I hope this helps some crafters out!