There are many things that change in game tone when you make the change from Warlord to Regent. For the most part, almost all aspects of the game have to be handled better in order to succeed at the Regent level. Longtime Monarch players themselves tend to find Regent a bit of a bore, since it's too easy, but there are ways you can improve your playing. Generally speaking, it's possible to seal the game at Regent right from the Ancient Age, with or without your UU, so it's not really that difficult. What separates the skill levels is more knowledge of game functions and accurate turn-based estimation.
The thing to remember when moving into Regent from Warlord is intelligence. You can't ever have enough of it. Even at higher difficulty levels, the info-gathering skills you develop at Regent will form the foundations of basic play. The chief sources of information you will have are these:
1. Units. Of course, units have sight range. Get your units out there! At Regent, it doesn't really matter much whether you annoy your neighbors by encroaching on their land, just expose as much of the map as posssible. Early in the game, it is essential to build as many Warriors and/or Scouts to find valuable resources, barbarian goody huts, and rival civs. Units also reveal more information based on where they are. A unit on a hill reveals more information than a unit on Plains and a unit on Mountains reveals most of all. Try to factor these into your exploration.
2. Cities. It seems a truism that your cultural borders provide you with information, but at this level of the game, the number of people who ignore what's right in front of them is astounding. Know what's in your borders. If there's something you don't know the nitty gritty details about, click the info available in the civilopedia. You just might be surprised by what that cow icon represents.
3. Diplomacy Screens. I'm not talking about Investigate City options here. I'm talking about the negotiating table. Once you found an embassy in the enemy city, all his city names and resource abilities automatically offer themselves to you. It's easy. If you can offer them Iron (even if you have no excess Iron), then it means that that civ has no access to Iron. Simple, no? Same goes for every other strategic and luxury resource on the books. The Diplomacy Screen also tells you how much they have in their treasury, and the advisor tells you what units they have or trades they can make. The tech trading options tell you how far behind you are or how far ahead you are, depending on the situation.
There are subtler sources of information, too. Generally speaking, a civ will offer to pay you money for RoP agreement if you're bigger than they are, and expect money from you if they're bigger than you. If you can extort money from then from a RoP deal (you have to change the offer; they'll always make a deal cheaper than what they actually are able to accept), then you're bigger than they are, generally.
When you get Printing Press, Comminication deals tell you how far they've explored. Basically, everything in the Negotiating Table screen yields information. Use it.
4. Advisors and info screens. Many people will tell you the advisors are bad and frequently off the mark, but you have to be able to use them first for you to make this judgement. The cultural advisor is usually spot on, and the military advisor is usually in the ball park figure. Both the advisor and the AI estimation usually value attack more than defense and bombardment ridiculously low, so be advised. You can actually use this in your favor. The city info screen expedites taking care of revolting cities. Just order them by production and look for the least productive cities. City info (F1) also tells you at a glance which city is producing what on how long a timetable. The overview can be useful when estimating the timing of an impending war. You can also change city production on this screen, so if you want to coordinate city production, this is the screen to do it in.
F2 is the trade advisor and tells you at a glance which commodities are exported and imported to whom. This is a better screen to evaluate ongoing trades than the Diplomacy screen, which requires you to toggle specific civs on and off to look at their individual trading specifics. It also tells you how much of an excess you have.
F11 is the Top city rankings. Early in the game, you can use this screen to find out which civs are your enemies and to indirectly find out what they're up to. A captial which doesn't seem to be growing isn't something to necessarily be happy about. Chances are, it's been cranking out Settlers. If you visit this screen diligently, you can usually count how many Settlers and Workers the enemy has been making in his capital city. The stats screen is also on this screen, for what its worth.
5. Exposed map areas. Whether you keep an eye on them or not, exposed map areas yield information over time. This is one of the reasons why revealing maps is important. Even "grayed" portions of the map will reveal strategic and luxury resources, railroad developments (in time), and gross terrain changes. Of course, putting units to scout constantly is better, but it's a mistake not to review the map, even if you don't have unit information.
6. Special buildings. Outposts (available after getting Masonry) are useful for keeping tabs on enemy movement as long as you keep them on Mountains. This is good both for defending against nearby AI and for planning offensives. You can usually locate an Outpost within sight of 2 enemy cities (the sight range is an impressive 4 on a Mountain) and you can then keep continuous tabs on what's defending it and troop movements around the area. This is especially valuable just before a war. You don't want to be on the wrong side of a massive AI defense upgrade.
