Creating a "base save" game file

When I did it, I did all the community Lots first. I made Magnolia Promenade and Windenburg my main community centres, put some fake career Lots in Oasis Springs, added a few parks in other worlds, a couple of clubs in San Myshuno and then the rest was houses.

I added the houses in world by world and section by section. So, I started with the 'cheap' area in Willow Creek (making them over with the same external wall coverings and roof slates) and then a 'medium' area for slightly bigger homes and then the more luxurious area with expensive homes, and then on to the next world and repeat.

So, for instance, this is my Willow Creek, which has one park and no other community Lots:
https://dl.dropbox.com/s/eo91cxr0dkj6c7v/World_Willow%20Creek.jpg?dl=0

And this is my Windenburg, which is one of my main community worlds:
https://dl.dropbox.com/s/qaugynkd5h8lwtm/World_Windenburg.jpg?dl=0

Then I placed all the pre-mades and all the sims I had made into homes, made sure they all had jobs and were in clubs, set up the seasons holidays on the calendar and then saved it as my base game ready to play.

My few tips:

Save often.

Upload assets you create to the gallery for easy retrieval and copy/paste usage. Things like bathrooms, stairwells, bedrooms, etc.

Create an apartment lot and place multiple copies of it in the world. This way you can have lots to house 8 separate sims. (Really good for placing sims you want as dating options)

Use venues that are multiple purpose, like a gym, spa, and bowling alley all in one.

Make community lots for skill gain. Like an arts center with easels, music instruments, a community garden, etc.

Make sure you have at least 1 of each venue. For example the lounge. The game makes elders hang out at lounges, so if you ever play an elder sim you will have a place for them to meet other elders.