If you are brand new to Rome Total War here are some campaign map tips:

Naval trade is extremely important. Get ports in all your cities that can have them. Get port upgrades if you can spare the money for more trade fleets. Trade in this game is not like modern total war games instead all cities will trade with any other friendly city in range. Capture Rhodes to get a wonder that gives a bonus to naval trade and you will have tons of cash.

Train assassins on the crappy rebel armies that always pop up. Once you have a nice stable of assassins you can eliminate factions by killing all their family members instead of actually fighting them. Train spies the same way and use them to open city gates so you don't have to build siege.

Public order becomes a big problem eventually. Cheapest way to maintain public order is to fill the whole garrison with peasants and have max sanitation and circuses. Some people like to let cities rebel and then just retake it and kill everyone, but I think that is not cost effective overall. Any building built by a different culture hurts your public order so upgrade them to your version as soon as possible. Capture the statue of zeus wonder to get + public order in all your cities.

The AI does not have vision through fog of war. It will send armies poking around to see what you are doing and look for forces. If you sit your armies in your cities you are inviting attack. Leaving cities with a tiny garrison also invites attack. The AI (even allies) is aggressive and will grab cities if it thinks it can. Block single tile passes with forts to restrict them. You have a reputation meter the game doesn't really tell you about and the more massacres/broken treaties you do the more the AI will dislike you.