How do I increase the quality of the players

You have a coupleasant of ways. First you will use the training grounds. Also, every map match, champ match and tourney match will help. You will see your players have numbers beside them in training and that means you have points to put toward attributes.

You should also focus on allocating training points in the right areas rather than just auto allocate.

Good plan is to get ur guild building up and running so u can join a guild as they will be able to help u out and u will get more advice. The guys will help u out on here as well

I cannot agree more with this. As rating is given only for the average star rating of every single attribute, a 50 star player may very well be less effective to your gameplan than a well built 30 star player. The old adage 'jack of all trades, master of none' comes to mind.

I've noticed recently that I have been scoring wins over higher quality teams, and when I check the individual player stats I can see why.

A classic example is I try to max out what I determine to be crucial and redundant skills for each position, and allocate my skill points accordingly. No need to have skill points for a back wasted on scrummaging, forward on kicking etc.

That's the goal, keep growing