I always make sure my players are on 95+ condition before a match. I rotate my team a little, particularly for some players whose condition seems to drop off a cliff after a game. Going into a game with just 80+ condition won't cut it. After 30 minutes of play, they'll already be at 60% compared to the opponents who will be on 80%.
Don't push the training too much. The major benefit you're looking for in terms of training are the team bonuses for attack, defence, etc. After each season, it's likely you'll ditch a lot of players, so personally I don't see the point in continually training up your favourite players because they get old, they train slower over time, and you're better off selling them on and dipping into the transfer market auctions.
This is my first season and I've already won the cup. I've technically won the league as well because there are only 3 games left and I'm 11 points ahead of 2nd place. I haven't spent real money to play the game. I sold half my team (over the month) and replaced them with better players. I bought players around the 28-31 years range, as it was easier to win the auction. I managed to get a 5 star MC for just 1 token - I know that doesn't sound great, but considering my best MC at the time was 3½ stars, it's a big jump.
Also, think about your formation. When I started playing, I always went with attack and I tried a 4-3(wide)-3 in one game, which was a disaster, and I lost 1-5. After that, I realised that it seems to be more about possession. So I've started using a narrower midfield. If the opponent is playing narrow, then I'd use AML/AMR; otherwise I'd use ML/MR. I've not lost a league/cup game since then.
Even against weak teams, I resisted using attack instruction unless I was playing at home. I'd also resist a light midfield - ultimately, if you can get the ball, you can create chances. I beat teams that were just 10% weaker by using Normal instructions, playing through the middle (because I pack the midfield), and won two of them 8-0, and another one 7-0. My I was playing just ONE striker, and he wasn't the only one who scored.
So think about that - goals do not just come from the ST. I've beaten two teams that were 20% stronger than me by deploying an AMC as my only attacking player. Obviously I parked the bus and played defensively. But it worked. So team formation is actually more important than a lot of the other stuff.