Learn to eat healthily on a budget. Buy cheap foods, such as oats, brown rice etc...
Have more nights in with a few cans of beer with mates, instead of going on expensive nights out to pubs and clubs.
These in particular are big ones. Cooking from scratch is so much cheaper than buying ready-made meals our eating at a restaurant. Likewise, drinking out is far more expensive than a night in.
I find keeping an eye on bank balances through mobile apps helps.