I'd suggest practising transition from bike to run as there's usually a line you have to dismount by. Use your spd's on the bike and trainers for the run. It's going to feel like you've been given someone else's legs
the most important thing is to practice the bike/run bits together as it needs getting used to.
You can get a tri suit in Aldi this week for £14 if you are quick. The mesh bra inside may be enough if you are v small of nork, otherwise wear your least padded and most synthetic sports bra underneath. Elastic laces for your running shoes (I favour the lock laces) make transition easier, and you'll need a race belt to pin your number on. For sprint, some people will wear run shoes to cycle in, but I prefer my spd sl shoes as the extra power on the bike makes a difference as its the longest leg
Read the race pack really, really carefully. You don't want to get disqualified for drafting, getting on the bike before the mount line, touching your bike before your helmet is on etc. Or not noticing that its a split transition and your run stuff is back in t1.
It's been a while as the tri got put off, but I did my first triathlon today! I'm exhausted but feel amazing! All your advice was brilliant so thank you. I'll be at Bodiam in September and hopefully will manage to be slightly speedier next time.