When you founded your first city, it built up pretty slowly. But everything was new for you, and you were learning as you went along. When you send out settlers to found a second city, you’re going to go right back to the start again with that settlement – it will build up very slowly.
How can you avoid this? How can you make building your second settlement – and third, and fourth, etc. – less of a chore at the outset?
The easiest option is to get your Caravans lined up, so that you can ferrying supplies to your new settlement. Use ‘vans to pump resources from your first settlement into your new foundation. Just keep sending the Caravans in, prioritizing your Storehouse (so there’s room to store their bounty), and you’ll be able to start building the interesting buildings (Barracks, Market, Consulate, Mage Tower; and from those, military, trade and diplomatic units) much more swiftly. You won’t have to wait to slowly build up all your basic resource production slots.
This requires you to have good resource production, and a fairly advanced Market in your initial city, but it will make it much faster to grow subsequent settlements. So, as you start approaching the point where you’re going to found a second settlement, make sure you are building up your Market.