Making line-ups is important. If you have weaker players you'll probably lose anyway but if it is somewhat close, a line-up can make a big difference.
Try different line-ups and use the analyse function to see what works. Keep in mind the result depends on a lot of random events, so looking at just 5 possible outcomes may be misleading.
There are some positions that are worth considering. Having at least one strong defender at the DCB position is a good idea because he will always stay back. A good defensive midfielder can also be useful because he can stop attacks before they reach the dangerous zones. Using the flanks can also work well, especially if the opponent has weak flanks.
Having too many defenders can work against you because too much of the game will be played in your defensive zone. This gives the opponent more dangerous free kicks and corners and maybe even penalties.
Having similar players on similar positions can make one of them useless because they'll both try to perform the same tasks.
