Build Up Your Fortress
One of the more obvious ways to play more defensively is by building up your base. The bigger and stronger the base, the more damage it can take and dish out on foes. The fortress has turrets that will fire automatically when enemies get near but you need to build it big enough.
You'll start off with one turret before getting more added to the base' arsenal. By chopping wood, you're contributing to the thickness of the base. The bigger the better as they always say. Hold your finger down the part of your fortress that you want to upgrade and wood will be deducted.
This is very important to getting wins, as by getting your base destroyed, you will lose. So making sure that it's sturdy enough is something that can be critical in who wins or loses. No base is safe, regardless of size, but adding weaponry makes things a bit cozier.
Deploy of Archers
This is an interesting tactic in Red Reign because this seems more offensive than anything. With that being said, this is a good way to create some defense too. As you can imagine, when archers are deployed (if you're the Human team), they fire arrows when enemies approach.
Knights on the other hand will charge into the waves of foes and take a ton of damage with many of them dying in the process. Archers are both good attackers and defenders because they can deal damage while keeping their distance.
Yes, these characters will die faster when approached, but by training and using a chunk of them, you will be able to eliminate many enemies without them getting too close. So definitely feel free to use some of those coins you collected from mining on some archers.
Finding The Balance
Sometimes, just finding some balance in Red Reign can be a great defensive tactic. Knowing how many archers you want to use and how much wood you should gather and different things like that. Sometimes it can be tricky to find the perfect balance.
You might spend a ton of time chopping wood to grow your base but may forget to add some extra knights or archers (again, if you're the Human team as other faction use different warriors). Or you may do the opposite and deploy many knights and archers but forget to grow your fortress.
A decent strategy would be to have many warriors ready before you chop wood. Now, just keep in mind that you need to mine for gold in order to train your army and put them in position. Do these things at a fairly balanced pace and you'll be gravy (and mashed potatoes).