A good way to get the best out of the 4-3-1-2 is to use it's flat three man midfield that it encourages to fight and win possession. The attacking midfielder links up with the two strikers in a narrow slot that often leads to through passes, clear-cut chances and goals. The full backs provide width down the left and right hand side, whilst the three man midfield stays central, and are basically the defence of the midfield. Offloading short passes, and keeping it simple. Doing their jobs.
I personally would suggest playing a high defensive line, that encourages aggressive tackling, pressing high up the pitch and making it difficult for the opposition to start attacks within their own half. A 'Stopper-Cover' combination between the two central defenders would be a good start, whilst one (or both, whichever) of your full backs are a Wing Back. Full Back on Support works fine. Then, edit his Player Instructions to make him 'Roam From Position', cover the 'Whole Pitch', and cross from the byline.
The other can have the same, and provides good width. Narrowing the formation makes the midfield compact, and lot more difficult to get through. I would suggest using two Ball-Winning Midfielders, on Support and Defend, and either a Box-to-Box midfielder, or a Deep-Lying Playmaker. Defend or Support - doesn't matter. You can have all three roles in the midfield, you don't have to had two ball-winners. I would suggest setting the passing instructions on the ball-winning midfielder(s) to very short, and the best passer of the three to moderate passing.
The attacking three that involves the AMC, STCR and STCL should be; Advanced Playmaker, Support/Attack (Trequartista is also advisory) Advanced Forward/Complete Forward, Support or Attack and/or Deep-Lying Forward, Support or Attack/Poacher. Those combinations are the most common and successful of such, and often work well.