I reply to invitations immediately and write them on the family calendar.
We've got cork noticeboards in the study - go through and chuck/file or shred things weekly.
Keep a box file for paperwork - don't put into dividers, just throw the bills, statements into the box. Get a new box file for each year.
The dc have their own laundry baskets and I wash each person's clothes separately, tumble them and put them away. Get out what you want to wear and iron it each day - takes 10 minutes tops.
Keep a bathroom spray, rubber gloves and cheap kitchen roll in each bathroom cupboard - I usually give the loo and sink a wipeover after I've been to the loo.
Delegate - dc have chores they're responsible for - putting own stuff away, loading and unloading the dishwasher, putting their clean clothes away, laying the table.
Deal with post as it arrives - get a shredder, a box file, a noticeboard and a bin and it's easy to do straightaway.
Do housework when you see it needs doing, don't leave it to do in one session - a quick polish of the banister when you're going upstairs, clean the mirror after your shower etc.
A mini hoover is a God send - clears up crumbs, does the skirtings and stairs without lugging the big one round.