For each match you play, you spend something like 60 to 80 coins on contracts. To save a few coins, you should pay attention to the following tips:
For the same price, always choose the contracts’ items that give you more matches;
Do not use contract items with many matches on players/managers who you do not know if will be in your club much more time;
Do not waste contract items if it exceeds the 99 matches;
Only make substitutions that are strictly necessary;
Buy a few managers besides the main one;
Only assign a manager to your squad if you need him to improve the chemistry;
Buy contracts during important promo packs releases, special In Form releases, and when weekly rewards are out;
Analyze the relation price vs the number of matches.