Well before I start, I certainly dont claim to be a great FM player, nor the best out there. I just have passion for football and Ive had some proper success in the game, including getting Cheltenham Town to the UCL knockout stages. Here, I discuss some points I never (or always) do, and which I feel people have some misconception about.
1. Dos
a. Always fill your preseason with games, against very weak opponent.
If you are a weak and poor side, you might be tempted to play against the big dogs for some easy cash. However, it isnt fun for our team to go to Anfield or Camp Nou and have their backsides handed to them. Money can come in other ways. Having lots of preseason games will allow you to condition your entire squad physically as well as greatly boosting their morale, which will give you an edge during the start of the season
b. Create different "formations" without changing your "play style"
I usually have a 4-4-2, 4-1-4-1 and sometimes a 4-3-3. All of them have the same instructions and play exactly the same. The thinking here is that I want to focus on making my plan A perfect, and by just changing the players positioning you are combating your opponents strong points without changing your preferred play style, which once again gives you the edge.
c. Analyze players stats
Is your anchor man not intercepting a lot? Is he losing too many headers? What about his passing completion? If they are bad (bad here means not showing how your style should be) then it is either the player isnt performing or not suitable for the role.
2. Dont s
a. Dont chop and change "tactics" during the season
Tactics here imply different formations and play style. It is like going from a tiki-taka style to an Atletico style defensive setup. Doing so during a season will severely hurt you.
b. Always discipline your players
Never back down from fining your players for bad performances or bad discipline. On the long run, you will find less problems and more consistency
c. Dont use a lot of TIs, OIs and PIs
While building your tactic, dont light up all the buttons in there. Use them to fine tune your tactic. For example, while building my defensive Atleti style 442, I began by setting the formation and the mentality. During the games, I found out that the D-Line isnt deep enough, so I introduced the drop much deeper instruction and so on. Regarding the PIs, I believe that if you use a lot of them, then you originally assigned the wrong role for the player. Try to keep the instructions to a minimum
d. Never keep a player against his will
He doesnt want to play for you. End of text. Given that you find a fair price for him, dont hesitate to load him off.
e. Dont buy players without thinking of your tactical setup
Dont buy Ibrahimovic when you play a false 9, or Coutinho if play an English style 442. Have that Klopp mentality and think carefully before getting someone new, and check if you can provide cover with your existing players.
f. Never use ready made "tactics"
I put the word "tactic" between quotes to emphasize how wrong it is being used. Tactics arent plug and play. You build it around your own vision. Some people arent competent tactically, so instead of downloading the "tactic", I advice reading the intro of the "tactic" and understand how it is build and how it works and build your own version of it. Try tweaking and improving based on your vision and your own players until you can later build your very own "tactics"