Some great ideas already. I instigated some sort of basic tidying up routine along the lines of toys-in-the-toybox when they were little but later was making a rod for my own back because I accepted they don't see mess, much less find it offensive, and probably don't have any clue as how to tidy up adequately... yet they had the wit to cherry-pick the least effortful chores to help with!
At this stage it's your job to do the serious cleaning and their job to tidy up after themselves. Both of them co-operate, everyone benefits, no more seriously fed up parent(s). One for all, all for one...
After the bedmaking and dishwasher they might move onto other things.
Write clear instructions, show them how it's done, where to access stuff.
Eg Kitchen floor or sofa gets covered with crumbs, get out the hoover, then vacuum.
Skid marks down the loo, use the loo brush and cleaner, scrub, flush.
Stinky trainers, leave outside, scrub in bucket, dry in sun, from time to time apply anti odour spray.
It may be a while before they automatically tidy up after themselves, honestly, no matter how many times you tell them, it'll fly out of their minds whereas the chart idea (and a small reward) can really help them focus.
You'll do them a real favour by encouraging this before they leave home, whenever that is.
PS I was watching the Royal Marines commando training programme on Channel 4 the other night, age of recruits ranging from 18 to 32 - the Army certainly thinks hygiene and tidiness is vital for self discipline. The language is rather ripe (!) for your 8 and 11 year old but the message was very simple, get a grip and do things properly.