Also helps to try to remember guys you've dealt with (whether accepted or not, if they reply with a reason that helps a ton).
For instance, Lellow is in one of my Leagues. I'm trying to offer 2 really good DTs, also really young... but I offered one of them to Lellow before and he doesn't use the kind of DT I have. My DTs are just to slow for him, so he's not interested in them regardless of how good everything else is on them.
So I shipped the Deal out to multiple teams, but didn't both Lellow with it because I know he's not interested in these type of DT. While he (well, he does now) doesn't know that I thought about him and his stance, and thus didn't waste his time with a Trade Offer, what he does know is he doesn't get a lot of Unwanted Trade Offers from me.
So maybe next time I have a Player he likes... and he's more likely to respond to me in a timely fashion if able because he knows I don't send him things that waste his times and I listen to his feedback, making the process much easier for all involved.