Don't waste time with people you know are not right/good for you and don't waste time worrying about it when you end things either. 
Pay into a pension monthly and make sure you keep up to date and accurate records of your contributions when you move jobs so you can also move your pension pot ( or better yet, use an independent pension and don't use your works one unless it's really good).
Make the time for the ones you love, regardless of how hard it can be, just a regular phone call makes the world of difference. They won't be around forever. :(
Wear whatever you like without worrying you're 'too old/ fat/ thin/flat chested etc, you'll NEVER be as young as you are again ! (even tomorrow you're older) 
Don't accumulate debt by thinking 'I'll pay it off later'', cos later never comes, and you just end up paying hundreds of thousands of pounds in interest for nothing.
Better to wait and save for things you want.
Enjoy your health, and do anything you've always wanted to as soon as you can, Bungee jump, travel the world, learn to salsa, take an exotic 5 star holiday............... whatever you've always dreamt of.........because once you have a DH or DC, what YOU want seems to slip away............................silently and unnoticed, until the DC are grown, and you realise you're too old/ unwell/ broke/ tired to attempt to fulfill your dreams now.
I'm very lucky because I DID manage to travel round the world for a year, work abroad, party hard and often, make lifelong friends and memories.............and I've never regretted any of it 