Running

Depends what your training looks like at the moment. If your mileage is low, you can progress just by running more; running 4/5 x/wk is better than running 3 x/wk, and getting a weekly long run up to 10 miles is better than only doing 4 or 5. 30 miles/week is better than 20, etc.

If you feel you've got a good aerobic base and/or can't spare any more time than you are at the moment, then you want to be doing some sessions specific to 5k pace, which can include intervals, e.g. 6-8 x 800, 4-6 x 1km, 3-4 x mile, but also some continuous tempo runs around 10k - half marathon pace, to improve threshold. A good weekly schedule might have 1 x interval session (3k - 5k pace), 1 x tempo run, 1 x long run and a couple of easy/recovery runs. If you're only running 4x/wk, maybe alternate interval and tempo runs, and just have the one quality session (plus long run) each week, because you want a reasonable proportion of your running being an easy pace.

So it depends what your schedule looks like at the moment. Get your miles up if you can, and only add in extra quality sessions gradually.