Organisation and de-cluttering!
I make lists... for everything. I have different shopping lists, one for the food shop, another for presents (which I add to when I randomly think of things), one for household/diy needs, and then separate lists for each major store I may shop at occasionally (i.e. I may put lounge cushions on the Dunelm list, so that I know what I want next time I go there, which may be a few months away). It means that I don't end up wondering aimlessly around Wickes or Dunelm or M&S or Currys trying to remember what I wanted a few weeks/months ago!
Lots of organisation, such as small compartment units, small drawer units, pull out baskets, etc., for stationery, kitchen gadgets, etc. Not only does it make it easier to find stuff that isn't used often, it also highlights when things are running short, as a trigger to buy replacements (put them on the relevant shopping/store list). We've kept things like old cutlery drawers from previous kitchens and put them in the garage to organise small tools, screws/nails/nuts&bolts, etc so neither me nor hubby have to rummage through tool chests for the small stuff!
De-cluttering is a biggie. We are very strict on only keeping stuff that is either of high sentimental value or high useful value. With paperwork, we just scan and shred it, so we don't have a single paper invoice or document in the house - all backed up to dropbox. With incoming mail/post, we either deal with it straight away or if it's something that doesn't need attention, it goes straight into recycling bins. We're very harsh with things like old videos, DVDs, CDs, books, etc - we keep nothing - once read/watched, it either goes on ebay (usually as a bundle) or goes to the charity shop. All our old holiday photos have all be scanned and uploaded to dropbox and the actual photo albums ditched. We purposely don't buy cheap crap like a load of cheap naff christmas decorations, or lots of silly signs/mottos or naff ornaments, etc - not only does it save money, it also means less cleaning/dusting! It's so much easier to dust a shelf or window-sill that has a few specific keepsakes rather than full of cheap naff clutter! Same with photos on walls - we have just 1 or 2 per room - again easier to clean/dust if you've less clutter.
Yes to a previous poster for having all "long term storage" stuff organised in boxes, labelled and listed, before going up into the loft! Same with DH's "big" tools and power tools etc - not all just thrown into the shed or garage - he has it all organised in large plastic storage boxes, labelled and listed, and stacked neatly in the corner of the garage - replacement/off jigsaw blades attached in a bag to the jigsaw itself, drill bits in small storage boxes in the same large box as his power drills, etc.
The amount of time saved by just keeping and staying organised is immense and it also eases the stress of searching for things, the risk of spending money unnecessarily on replacements for things you already have, but can't find, saving the wasted time of wandering round shops trying to remember what you wanted or wasted journeys going to shops specially for something you'd forgotten etc. Life is so much calmer and stress free if you're organised!!