This is mostly common sense, I think, but I feel as though it is often overlooked, and in my own experience the fact that it is often overlooked is why FFL trades are so rare. I will edit this with quality strategies offered in the comments.

Step 1: Identify your needs

This goes without saying, but is nonetheless the first and most important step. Trading is about improving in areas of need, and targeting players on other rosters who fulfill those needs. Whether due to injury, lack of performance, or a lack of wins, the first thing you must do is find where your needs lie.

Step 2: Identify your strengths

This, too, goes without saying, but again, it is part and parcel to making a trade work for both teams involved. If you are strong at a position, seek to maintain that strength by keeping those players (except to upgrade them). You can hardly expect to pull off a meaningful trade if you haven't both identified your needs and identified your strengths.

Step 3: Identify your excesses

Again, an obvious requirement, but this step is also crucial; with your needs and strengths identified, your excesses tell you what you can afford to deal away. There is subtlety here, however -- your excesses are not always on your roster.

If, in a 12-team standard league, you have the #4 QB as your starter, and the #10 QB as your backup, your backup is necessarily better than the starter on at least three other teams. That backup is an excess. If your starting QB has not had his bye, you might be inclined to think you need that backup, and might not include him among your excesses -- but check the waiver wire: if the #14 QB sits there, the odds are very good that a) your #10 backup is not appreciably better, b) the #14 QB might be better than the starter on three or four teams (because of byes or QB hoarders), and c) you can easily afford to move your backup and pick up that #14 QB. That extra QB is in fact an excess, even though you may very well need a backup QB for your starter's bye week.

Identifying an excess, then, is not merely about spotting startable bench players on your own roster, but about spotting quality roster-worthy bench players on the waiver wire who are comparable to those players already on your bench. This doesn't mean the popular waiver pickup du jour should count, mind you, but that players who are unlikely to be claimed via waivers should be considered part of the available player pool for your team -- free agents are everyone's players.

Side note: It's perfectly acceptable to target as one's 'need' another excess. That is, if you have several start-worthy WRs, but only a couple quality RBs, you might trade away a WR or two for another RB (or two), just to generate an excess at RB, which could in turn be parlayed into a trade for a superstar WR or a significant upgrade at RB (or whatever). Your 'need' from Step 1 isn't just where you presently suck -- your ultimate 'need' is to win your league's championship, and the whole point of trading is getting you closer to achieving that.

Step 4: Target teams with whom to trade

Many FFL owners skip this step, and proceed to targeting players. This is a mistake, and this is where I expect this tutorial to prove helpful. Targeting players is of course necessary, but it should come only after targeting a team. While you may well need an upgrade at WR, and you may well be able to pull off a trade with a team which provides such an upgrade, you'll enjoy greater success -- and better payoffs -- by targeting a team first. This process is basically the same as the first three steps, but applied to the other teams in your league, and comparing their needs and excesses against yours. You're obviously looking for a team whose excesses match your needs, and whose needs match your excesses. If you first target players, you may overlook this compatibility requirement, and as a result you may not maximize the value received while minimizing the value offered.

Step 5: Identify the most beneficial trade for your team

Ahh, the douchebag maneuver. From among your excesses (which match the targeted team's needs), and among your prospective trading partner's excesses (which match your needs), identify the worst player to offer for the best player to receive. This is a candidate initial offer -- but don't make that offer just yet. In the best possible world, this trade would be accepted, and you could proceed directly to Step 10: Rosterbation. Hold steady, however, because it's not necessarily that simple. If this trade is too lopsided, your prospective trading partner may become offended, and they'll demand more value than you are willing to give. Patience, Daniel-san. You must learn balance.

Step 6: Identify the least beneficial trade you're willing to entertain

This is one of the most difficult steps; it's very difficult to put aside your bias or desire to trade-rape every prospective partner. The prospective offer you identify in this step is, if your prospective partner is following this guide or reasonably intelligent, quite likely the offer which would ultimately be accepted if you are each honest and forthright. But you're not. You're devious, and you're conniving.