I have been playing with this for a while now and have found the following to be the most effective way to aquire the top picks.
During a season i will dump about 3 average players, then sign 3 players all around 60-70 overall.
Then let the season end and go into the draft. Let the computer teams draft their top picks and go into the next season, but take note of the teams that drafted the top 5 or 10.
Before the new season starts go to trade players and trade the 3 that you picked up the previous season (or whoever you want to get rid of)for 3 of the top 10 that were drafted(it doesnt have to be 3 it can be whoever or how many you like).
This generally works as the rookies are not proven and the players who have experience and are around 70 overall are well regarded.
Try it, it works!