To win the Tier 1 championship you must first win the Tiers 3 and 2 championships so this guide will cover all three.
I chose to use Atlanta for this achievement, however to make this easier I customized a few players. To do this on the main menu go to Create>Player Editor>Edit Attributes. You can customize every player on the team to max if you'd rather be safe than sorry. however I personally found it unnecessary.
I maxed out my starting Quarterback and Running back to max stats. Then maxed out my top two Wide Receivers, my top 5 Offensive Linemen and my kicker. To put it more simply I purposely made the offensive side of the team the best part and relied on them throughout to just outscore their opponents. If you really are struggling I'd suggest to do both sides of the team to cover all bases.
Now to start a Franchise go to Franchise Mode>Create New. Be sure to pick the team you chose to edit. Before starting be sure to set unlimited fund to ON
. This is very important as you will need to retain your players each year if their contract is up after the season.
When you are in the Franchise menu under actions you have a choice to either Play, Coach, Spectate, or Simulate a game. For the regular season you can simulate each game one by one and ensure that you win at least 12-16 games per season. I personally went 16-0 for the first two seasons and 13-3 in the third season.
Once you make playoffs hit spectate game, and under Game Setup go to Rules and change the Quarter Length to 3 minutes to make this process faster. Repeat this process for each playoff game. Now if at any point during the game you feel that you team is going to lose, restart the game by hitting
>Game>Quit. Then go back into the game and repeat the process. The load time for this game is decently fast so this won't be to lengthy a process.
After playoffs you will have a list of actions for the offseason such as Draft and Player Contracts. You will need to complete this in order to start the next season. For the Draft you can just pick whoever you wish for all 7 Rounds. After completing the Draft go to Player Contracts and you should have $999M for available funds so resigning all players should not be a problem. Now you can choose to sign some free agents if you'd like to. Try to aim for players with a least a C+ rating or better. You can now continue to the next season.
Rinse and repeat this process of Simulating, then spectating each playoff game and all three Tier Championship achievements should not be a problem.