You have to be careful not to go too fast too soon. I prefer 800’s if you think you can do them. Start with 2-3 of them if you can at 5k goal pace with 2-3 minute rest in between. If you do 400’s shoot for 10-20 seconds faster than 5k race pace and start with 4-6. Ideally I like to build up to 3 by 1 mile at 5k goal pace or 5-10 seconds faster with 5 min rest in between. Nothing magical happens on race day. You need proof of work to build your confidence! Go get it!