It really depends how old your pre-schooler is. I have DS1 who is 3.10 & DS2 who is 1.6. I work 1 long day per week (12 hours+) and am home with them the other 4 days. DS1 goes to pre-school for 3 hours each morning during termtime, although by the time I drop him off & fetch him, I have more like 2.5 hours without him there.
My main tip is to try & do things as you go along. So, if you are going upstairs eg to the loo, take something with you that needs putting away. For example I sort the clean washing into each person's pile & take 1 pile up with me & put away each time I go up. Takes 5 mins per pile rather than 20 mins altogether so seems more manangeable.
Along similar lines, if I am boiling the kettle for a cuppa, I empty/stack one half of the dishwasher whilst I wait for it to boil.
While the kids are in the bath, I clean the bathroom except for the bath which they are in.
If I have to pop out to the garage or to put bins out & don't want DS2 to escape, I put him in his highchair with In The Night Garden a book for 5 minutes.
If I want to do some sorting upstairs, I bring DSes up with me & DS1 plays in his room, while DS2 has a basket of toys at the top of the stairs which he likes to play with (stairgate firmly shut).
One final thing is that we get out of the house every single afternoon or day when DS1 is home, whatever the weather. It could be a walk to Tesco or a trip to the park or soft play, but I find it wears them out & keeps them happy. I am very lucky that both still nap around 1-1.5 hours, but I don't tend to do housework in this time, I consider it my break, as I am on my own with them for 12 hours most days & often more (DH in TV so very unpredictable hours when filming).