3) Run Underworld Trading Missions. Each mission has a level range, (ie, 41-48) and if you receive a critical on that mission, you have the chance to bring back a schematic within the level range of the mission you ran.
So if I am getting it right, if i want the full Aspiring Knight set i need to run the UT missions from lvls 11-16? To match the set required lvl?
For this particular set 11-16 missions will give you the whole thing, because all of the pieces are in this range.
Unfortunately this is not always correct, because when they rolled out the catalog of orange sets, they couldn't be bothered to make all the pieces in each set the same level; in many cases they're not even in the same "range." The Commando's Boots and Gloves, for instance, are level 15, but the rest of the set is level 19. Even the "level 50" sets all seem to have one piece that is randomly level 47 for no apparent reason. So you have to know the level of the particular piece you're missing, and make sure you're running missions in the range that covers that level, otherwise you'll never get the full set no matter how many missions you run.
And how do you know the level of each piece? Unless you already have the piece, or can find a schematic for it on the GTN, there is no way to know. Some pieces are the same level as the chest and others are not, and there is no consistency to it from set to set. Some pieces are in the same level range as the chest, and others are not. So you have to find out from somewhere on the internet, from GTN schematics, or from someone who already has the full set what range you need to farm for each particular thing.