That suggest you did not expand enough and did not have enough workers or did not use your workers well. It can be aggrevated by making structures in a town that cannot support them.
This you see often where a a town is making a lib. The town is the 12th town or so and is size 1. It is not growing or is growing very slowly. No value in the lib as you have 1 beaker and can not gain another from the lib right now.
Worse the town will not net many beakers for some time and may be stuck at size 3 for a very long time and never need the lib.
I reviewed lots of games where I see towns that have a temple, lib, barracks and maybe other structures and are stuck at size 4 or less and may even be very corrupt. This cost money for maint and it means shields went up in smoke.
Workers, you basically need enough to come close to being able to improve tiles that are being worked, close to the time the pop is created to work the tile. This is only critical for the core, but you at least want to get some roads in the outer areas as well.
Evalute the tiles and prioritize them for workers, see Crackers Opening thread for how to evalute tiles.
Wonders that you have going that are completed on the IBT, means you have to switch to something else as you can no longer work on the wonder. It is built elsewhere. Best thing is to learn to properly determine what wonders to build, if any and what your chances are to be first to complete it.
This is easy as you know how many shields it is for a Regent level AI and for you at all levels. What I mean is a 400 shield wonder is 400 for you, but for the AI it cost a value based on the level. Lower cost for the AI above Regent and same as you at Regent, IOW they get a discount above Regent.
So you just have to figure the turns you need and guesstimate how many for them and know when they have or will start. If you make a net 10 shields on a 400 wonder, 40 turns (if no tiles change).
If they have the same 10 turn town and are on Regent , you just need to start first or improve your shields faster than they do. If this is Sid they only need 160 shields, you do the math.
Two ways to beat them at a wonder that you can consider.
1) pre build prior to learning the tech
2) (can be combined with 1) Increase the shields per turn.
This can be done in two main ways. Get workers to mine tiles and add workers to the town, if it is less than max pop. You need to be able to feed the pop, so you probably cannot have all mined tiles.
War is easy as they do not know how to fight. First try to be rated as at least average to them to slow down the DOW's. Second realize that a fight is coming and get prepared. Do not make spears, if playing low levels, make only attackers. Make them in a barracks town for all but the first few, presumes not playing AW.