Firstly, it's difficult, but not impossible. Though there are multiple variables to account for, such as the strength of your team and your opponent's. Get this right, this is about as much of a pay-to-win game as you'll find, and if you can't invest money, and if you can't invest time, it's going to be a very difficult ride. But watching these ads for the training packs takes literally 15 minutes per day. You'll get times where the schedule is kind with plenty of time between matches to recover, and vice versa where you'll either be spending packs or going in unfit. For my first few seasons I put out a weak team for cups so that I didn't have excess fixtures. Also, choose your battles. The associations give good rewards and are worth the extra fixtures, the friendly championships do not and are not.

How to train efficiently - the concensus is that in order to hit your 40% bonus, you take all your players, and train them across 1 very easy and 1 easy session across all three disciplines. Do that 4 times daily (or twice with the 2x multiplier) and that will recover the 8% you lose daily. But you'll need to overinvest for a few days to get to 40%.

What I don't see a lot of people mention is individual bonuses and I think it's far more important than people give credit for, so having individuals at 10% really helps them play cohesively as a team.