Its time I tell you the correct way to use GTS
The most single important thing I can ask you to do is PUT UP YOUR OWN POKEMON INSTEAD OF LOOKING FOR SOMEONE ELSES. We'll go over that in a bit, but first, I want you to open up GTS and search for a Pokemon you might find in the wild late game or is easily evolvable.
Search for that Pokemon. The first things you'll see are the most recent offers. The most recent offers are always the best deals. Why? As you go further back you find deals from longer times ago, the deals get worse. This is because these are the deals people skip over, so don't dig extremely far back through untradeable legends to find any deals other then untradeable legends.
How does this help us you might ask; it helps us in two ways. First we learn that the further we go back, the lesser the chance that we'll find a deal that we can happily fulfill. The second thing we learn from this is that our submissions will be the first things we see, and the less easy it is to fulfill, the quicker it will move into the back. But over time, you'll see that legends like Xerneas are near the beginning of the bad offers, then legends like entei to Lugia, ending finally with unobtainable legends. Yes, this does mean your legend offer might be taken, but it will take a very long time, at most with popular and commonly uploaded Pokemon more then a month. We can improve this speed however, which brings us to submitting our own Pokemon on GTS.
If we put up our own Pokemon on GTS, it will begin life in the good deals, so people will see it first. The most common user of GTS you'll ever see is one that looks for deals. This kind of user vastly outnumbers the people who put things up. So by putting up your own Pokemon on GTS you ensure a quicker trade. People will look at your deal and do the trade rather quickly, making it a great way to fill your dex.
Keep in mind that the more reasonable your offer the quicker it will be taken
Don't be the fag in the pic related