If you want expansion, then you want one city that both grows and pops out 30 shields on the same turn.
This should also be a size 4 to 6 city, whatever you need to drop shields enough that the town will grow twice before spitting out another settler after each one it produces.
Using roads only on the tiles that you want your city to use will guide the auto-allocation toward putting the new laborer on town growth to work on the tile you want. Irrigate plains, always, or unless there are only hills and plains around, you won't get a laborer automatically put there.
City size 5 - build on grassland, surrounded by grassland, plains, and forest mix
Center tile: 3 food, 1 shield, 2 commerce
Second: grassland-shield; 3 food, 1 shield, 1 commerce
Third: grassland; 3 food, 1 commerce
Fourth: grassland; 3 food, 1 commerce
Fifth: plains; 2 food, 1 shield, 1 commerce
14 food production, requires 10 food - surplus of 4. 3 shields, so settlers come in 10 turns. You'll have a food surplus of 4 even when you drop down to size 4 (the object being to grow to size 6 the same time you get a settler).
I'm being really bad by not checking to make sure that with a granary you'll go from size 4 to 6 in 15 turns with a surplus of 4, but this is how a settler farm is made. Just do a little bit of mental math, note how fast you're growing and how many shields you have, and by all means make use of bonus resources like cows!
Get your second city doing this by the time you found your 5th, then another city doing it by the time you have 8. Just get 15 cities founded and you can lead in whatever you choose to in a Monarch or below game, be that science, war production, gold, culture, etc.