7. Don't Buy Loads Of Players
Carrying on from earlier the scouting theme, there's always a temptation to bring in an absolute shedload of players to an already-burgeoning squad. In certain situations, this is acceptable when you've been unexpectedly promoted or when your elderly squad is on the verge of group decline, for example. However, you must always resist the temptation to recruit just for recruiting's sake. Sure, we all like the look of certain players, but its only when you're playing as a European behemoth that you can sign someone just to spite a rival (Ryan Shawcross still rots in my reserves on FM 13, take that Chelsea). If you have to live by more modest means, I'd recommend that once three first teamers could competently play a singular position (even if it's not their first choice), it's time to shut the negotiations. As Ian Holloway will tell you, wildly buying a bus-full of players comes with pitfalls they destroy the team dynamic, they take a long time to adapt to your systems together and they chew up your wage budget. All three of these can easily derail a squad, so usually, it's best to add sparingly, and early. If you do need the full overhaul, make sure all business is done by the second week of August any time after that, and you're going to run into problems. Come transfer deadline day, don't be the side Jim White'll stalk with an on-site reporter and an army of cheering loons be the ones with the gates shut and business concluded.