How to increase my league's reputation ??

what factors ?

European coefficient. The better the teams in your country do in european competitions, the higher you'll be rated eventually, as it takes past 5 years into count when setting ratings. It will propably be a fairly slow improvement as a result.

I can control my club, but not others....

I pretty sure it also takes other things than European coefficient into consideration when calculating reputation... don't know which though ;-)

You could try to sell good players to other clubs in your league, and not poach their youngsters. I used to buy the best youngsters in my league, but don't anymore, as the other clubs might do worse in europe because of it.

I can control my club, but not others....

You can in a way over time. Invest heavily in youth recruitment and development and you slowly increase the pool of national players. Not all of them will make your first team. Release and sell to rival clubs. Loan out young talented players to other teams that will be competing in europe.

As you start to make an impact in europe you will drag the coefficient up and get extra euro spots for your league. The money from that gives a big kickstart to the recipient clubs. The money you make from your own euro adventures also filters into the rest of the league via increased tv revenue if you start to drag the euro co-efficient up.

It is slow going but it can be done. Just don't expect it to be very noticeable year by year.