If you have the Outdoor Retreat GP, cloud/stargazing is a much more efficient/faster way to get a Sim inspired then taking a thoughtful shower. As soon as the moodlet pops up, cancel the action and it'll stay active.
If you have a Sim using the woodworking table and again own Outdoor Retreat, once your Sim reaches Level 7 (or 8?) travel to the campgrounds and study the large Camp mascot statue for a schematic. That way instead of making bathtubs which take 1.5 hrs. each to make, they can make a smaller version of that statue in just 45 minutes! It cuts your Sims woodworking time in half and make about the same amount of simoleans as the bathtubs.
If you like to play Rags to Riches style, but want to make some fast simoleans, travel to Magnolia Promenade. The fishing spot at the end of the pier is great for reliably fishing up dragonfruit and voodoo dolls. Voodoo dolls sell for 950 simoleans. If you fish up a cowplant and don't want to grow one, don't just sell it for 20 simoleans, plant it first. Immediately go into buy/build mode and sell it there for 475 simoleans!
Want an easy way to cut down on your bills? Put all your collectibles you want to keep, but not display on a Generic lot. Other Sims won't go there or steal your stuff and anything on that lot doesn't count toward your Sims bills. Same goes for retail lots. Sometimes I'll plop my Sim down on an empty lot then immediately buy a retail lot and live there without ever opening the business. You can build to your hearts content and have super low bills! Build a mansion and only pay 33 simoleans a month! Cool eh? :)
I always build a bathroom near or next to the kitchen. That way if one of my culinary challenged Sims starts a fire cooking, they can run to the shower quicker to put themselves out.
My Sims homes rarely consist of more than one level. It saves time from having to go up and down stairs. I like an open floor plan too for the living and kitchen areas.
That's all I can think of at the moment, I'll post again later if I think of anymore. Hope these are helpful! :)
EDIT: Thought of one more. Drinking water will fill your Sims hunger bar. Their bladder will go down quicker, but if you have a homeless Sim with no simoleans, no plants to harvest and no helpful platters of food cooked by other Sims around in a park, its a good way to fill their tummies in a pinch.
Also, as soon as I have all the appliances/electronics I want to keep, I upgrade everything. It takes a bit of time at first but will save heaps of time in the long run. Here's a hack for getting upgrade parts for free. Have them scavenge for parts from the trash pile you get when repairing something and then direct them to trash it. BUT, immediately cancel the action. They'll drop the bag and a new pile will be on the floor/ground. Scavenge for parts again, rince and repeat over and over. Voila! As many free parts as you wish.
It's a good idea to have the trash can far away from appliances though or sometimes you can't cancel the action quick enough.