You know the guy. He is the one who keeps sending you seemingly meaningless trade offers (except to him) day after day, week after week. I am not talking necessarily about an uneven trade like, "I will trade you Drew Stubbs for Carlos Gonzalez." Although I am sure we have all been the recipient of an equally bad offer. I am referring to the person who offers you Dan Uggla and Jordan Zimmermann for David Wright. He'll say, "Are these two guys even close to getting Wright, just don't know value." My reply, "Do I need a SP or a 2B?" His answer, "I don't know your needs."
Don't be this guy! If you don't want to be this guy then there are some measures you can take that will prevent it from happening. The best trades in fantasy baseball occur when all teams involved benefit from the transaction. While this does not always occur it should nevertheless be the goal of all involved. If you are shown to be the fantasy player that is looking to take advantage of people in trades that do not benefit the other team, you will likely find it difficult to find a trading partner.
There are a few things you should do before making a trade offer in your league. First analyze your team needs and strengths. You will likely need to trade from your strength to fill a need. Needs can be positional or categorical. Next, look for a team that is a good fit for those needs. When you find these traits you have found yourself a great opportunity to make a deal.
For instance (hypothetically); you have Lance Berkman who just went down with an injury, and you need a first baseman. You research and see that Team B has Freddie Freeman on his bench and Miguel Cabrera in his lineup. Freeman is likely expendable for Team B. You do some further analysis and find that Team B could gain several points in saves. You just happen to lead the saves category by a fairly wide margin and the loss of one closer would probably not cost you anything. You offer him Joel Hanrahan for Freddie Freeman, he accepts and you have both addressed your team needs.
By doing just a little research before making trade offers you can dramatically increase your chances of actually making a deal and helping your team. Of course you should be mindful to not help a team that is ahead of you in your league standings. Bottom line, "Don't be that guy!"