Plank
First of all, clear a little space – push back chairs or tuck away things from the hallway. If you have a yoga mat, set that up somewhere. It’s not essential – if you have carpet you don’t need anything, if it’s a hard floor maybe put a towel or two down just to protect your arms. Get into position: lie on your front with your forearms on the floor (parallel to each other), toes tucked under, then push up your bodyweight so you are resting on your forearms and your feet. Keep your body in a straight line – brace your core muscles, don’t sag in the middle. Hold!
Work up to holding 1 minute. If you’ve never done it before, have a google of “plank daily challenge” and follow that – in days you’ll move from 10 seconds to 60, and possibly well beyond. If you’ve already a regular planker (which sounds, to my English ear, horribly close to an insult, sorry) then try variations like side planks or harder adaptions. Check online videos for correct form but also always remember my own personal plank rule 1: while planking you must spend the time thinking about the fact that the world record for a plank is 8 hours and 15 minutes. It’s strangely cheering, mainly because no one is making you do it.