Before a game in franchise mode, go to the Owner's Box--->Set Prices--->Advertising. Set all the prices as high as they can go ($1M for TV, $500K for Radio, etc. Etc. Etc.). Play your game, then before you sim the rest of the week, go back to the Owner's Box and remove all advertising costs. You gain the benefit of the advertising without having to pay for it. Go back to Play Week, and sim the rest of the games that week. Repeat for all home games.
I am in my 10th season using New England, and have sold out 100% of home games for 9 1/2 years. You can also bump the ticket prices down a bit doing this, and STILL make good profits. Helps when you get to the off-season, and you need cap room to re-sign your star, or sign the top FA.