Literally my only tip for any family or friends going into uni is just to budget. Not only does it actually help you control how much you spend, but you'd be surprised how much stress it actually takes away. Find what works for you - for me, I used a spreadsheet to track how much I would spend each month; it wasn't actually as much effort as it sounds.
Overdraft is another issue that a lot of students face. It hasn't been an issue for me personally, because I don't get any :( But my advice based on what I've seen my friends go through is: DON'T. GO. INTO. YOUR. OVERDRAFT. It's so difficult to get out of!
With that being said, we all make mistakes sometimes and it's okay not to be strict with yourself all the time. It's also about enjoying your uni years too!
Download "Too Good to Go"; it'll save you tons of money on food and stop good food from going to waste at the same time!
When you first start, there is a lot of pressure to spend money. Most sports societies ask a lot to join and buy kit and activity groups often have membership fees. Go to the free tasters first and think about whether you can see yourself actually going to their training sessions or events before committing to fees. Even better, find societies that have free membership. (Like GP Soc, but also lots of others!)
It’s really easy to overspend during term time, so it’s a really good idea to set up a budget/expenses tracker. I didn’t have any idea how to get my head around an excel spreadsheet but there are loads of easy tutorials and budget templates on youtube!
Take your student ID card everywhere as you will be surprised at the number of shops and restaurants that offer student discount just by showing your ID card! This includes: Ryman stationery, Subway (on Borough High Street next to Guy's campus, one next to Wasabi; I only found out in 3rd year!, Leon, Wrap It Up and Superdrug.
A tip that you may not know is that if you have a 16-25 railcard, you can actually link it up to your Oyster card by taking both cards to an underground station and asking the staff to help you at the machines. This then means you get an additional 1/3rd on off-peal travel in London and the South East. Over the course of years at university, you will hopefully have saved lots!
The 'Hopper Fare' on buses also means that you can use as many buses for free within one hour, which is great, affordable way to explore different places or for commuting if you have to change buses.