Brief discussion of my primary tactic.
In the lower leagues, I primarily use a 4-4-2, which the FM engine describes as 4-4-1-1 DM Asymmetric. I use this formation because: it is balanced, I can use basic position roles, and I can find players to fit those spots. Situationally, I make adjustments to the tactical style rather than the formation. This allows for fewer training sessions to achieve a reasonable amount of tactical familiarity.
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I use four styles: Balanced, Counter (cautious), Advance (positive), and Press. I used balanced most times. Early in the season and in away matches, I use the counter. If I see that we are possessing the ball more than 60% of time, I switch to advanced. Likewise, if I see we are losing the possession battle, I switch to counter.
Usually in the last ten minutes of the first half, I'll switch to advance or press and use the shout buff of 'get creative.' If we're tied or behind, I'll switch to advance. If we're ahead, I'll switch to press.
If we're losing the possession battle or I see that the opposition has switch to a more attacking stance, I might switch my left fullback from support to defense. If we're getting beaten over the top or from through balls, I'll switch my central defenders to defensive vs the stopper-cover combination. If I am using squad players or facing a lot of pressure, then I'll put both center defenders into defense or change them to no-nonsense defenders.
The defensive midfielder role is flexible as well. If you can't find a defensive midfielder, it's easier to find a ball winning midfielder. Although it is a roaming role, on the 2D screen they generally hold their position ahead of the centerbacks. If you have time, convert a short mobile center back into an anchor man, and he'll provide cover for the back two.
Now for the most important defensive midfielder role. I use him to specifically mark an opposing player after he scores. Goalscorers tend to get on a roll. If a player is scoring, he is likely to either score again or create scoring opportunities. Thus, ignore warnings that your player is being pulled out of position, and use the DM to shut down the threatening player. If possible, pull the central midfielder back down into a DM slot. On the 2D screen, you'll still see both midfielders moving upfield in unison while attacking. However, the opposition will enjoy additional possession in the center of the park.
I caution against using BWM, B2B and AP together. Each of them is a roaming role. The 4-4-2 is vulnerable to center attacks when faced against a 4-1-3-2, and one can get overwhelmed at the top of the box. I much prefer to use a DM/Anchor Man combined with a CM-S as they can be instructed to hold position an occupy the center of the park.
On offense, I already have hinted that one can use an AP vs AM. I haven't used a shadow striker in FM19, but I used to use one in combination with a TM. I described above, how I use the big man-little man combination. Poachers are readily available, and in my setup, the AP becomes AP-S, where only a P-A is available. I have used a PF-S in combination with an AP-A, and I found this adequate with my personnel.
Ideally, I use a target man for the big man-little man combination. I find that TM-S comes deep and has a high pass completion rate given their hard coded short simple passing. I also find that a TM-S gets into enough threatening positions to lead the team in scoring while providing an outlet, a fine LLM alternative to the complete forward. However, you will see more than a few times, balls being passed into a space that would be otherwise occupied by an AF or P.
On offense, we have three players, the attacking winger, an attacking midfielder and the target man. Given the characteristics of the TM-S described above, this rates as two-and-half attackers, despite one player being on support duty. Where there is only a poacher available, swap the support and attack duties between the AM/AP and the forward.
What is not advisable is swapping out the winger or wide midfielder on attack duty. Despite improvements, the FM19 engine on defense remains vulnerable to byline crosses and overloading by three central attackers. Thus, I have positional instructions for my two wide players to cross from byline.
Speaking of positional instructions, I keep things simple and have a limited number of instructions. The only essential instructions are the aforementioned 'cross from byline', then 'shoot less more' applied to all attacking positions, and 'take fewer risks' applied to all positions except for one designated creative/roaming player. I find the 'shoot less more' individual option better than 'work into the box,' although it's a feeling more than something I can prove. I also use the 'take fewer risks' in combination with shorter passing to keep possession of the ball. I haven't tried 'play for set pieces;' maybe someone else can detail how that is working vs shorter passing/take less risks.
The only players with 'close down more' are my two central attackers. Using this primary tactic, I observed over two-hundred FM matches. I can only recall two occasions where my attackers were able to pressure a defender into a mistake that was converted into a scoring opportunity. It may be because I am not playing with defensive forwards, or maybe I don't have the right attributes. In either case, 'close down more' is optional.
For opposition instructions, I have instructions to tightly mark AMC and three striker positions. I am pressing the goalkeeper, central defenders, defensive midfielders and the side central midfielders/attacking midfielders. I am showing onto foot of all wide players. On the backline, my aim is to push them inside, so I show onto the opposite foot. In the wide midfield and attacking wing positions, I show onto the inside foot to push them out wide. The CM position has no instructions set.
I don't have a study to prove if this set of opposition instructions works as intended. I do know that the 4-4-2 is vulnerable to overloading from central positions, and I aim to press the non-forwards. I also know that in FM crosses are deadly. So I aim to prevent attacking fullbacks from running out wide, and work to keep attacking players from turning the corner for a diagonal run inside. I am tight marking the central attackers, and pressing wide sitting attacking midfielders.