My own tips
1 - Plan ahead
You can make a sucessfull squad without spending too much , before every season take in account the turnover you might make of sponsors and planned position on league / cup / champions cup and don't let your salaries be more than a 50 % or 75 % of it .
For example :
As bayern munchen I make about 35 million in sponsors , 15 - 25 millions from league positions and about 10 - 30 million off champions cup , that means I should have my salaries around the 40 - 60 million mark to make a consistent profit or , if thing go wrong , don't go in red numbers
2 - Youngsters Youngsters Youngsters
You can make a succesfull team just relying in your youngsters - Buy them when they're 14 - 19 year olds , they'll take crappy salaries till they're 25 - 28 , if they start to ask too much sell them and let the next guy in line take his spot - Don't only rely on your facilities , getting youngsters off other teams will save the day most times , Remember that buying and maintaining youngsters from minor leagues it's 3x times cheaper than getting those major league wonderkids that will ask you 1 million per year on their first constract .
3 - Keeping contracts under check
For the most part ambitious guys will ask you for their first big contract really soon and sometimes it might make your head ache a bit , the best way to combat this is to keep a low profile on salaries , for example , Ribery and Robben had a contract for 10 million per year and 7 million per year each , before their contract finished loyal guys like schwesteiger and alaba were asking me for 5 - 8 million a year contracts , after Ribery left I could sign schwensteiger for just 3'5 million a year .
4 - Balance
Following my tips always balance your team , I have been able to win the league and fell very short of winning the champions league with a first team under 20 million per year , but if you happen to fetch 3 or 4 wonderkids in similar years you might think of giving them the contract they want and win everything for 5 years straight , Your call .
Thank you for reading me and I hope it's been useful for anyone , Excuse my english as Im not a native speaker .