IFTTT is the simplest and most straightforward of rule designs, so if it’s not something you’re interested in, I’m not sure what would be. Most of the other options are more complex.
The most comprehensive rule management that does not require using third-party options: rule machine
If your concern is that you don’t want to go outside the SmartThings system, however, then rule machine, which is custom code, is a good rules engine which works entirely within SmartThings. It Does assume that you understand Boolean logic and can construct your own if/then statements, so it’s not for everyone. But if you are used to that kind of approach, it’s very powerful.
For that, you need to visit two forum topics. The first one is just the FAQ on how custom code is used. If after reading that you feel that you would like to try that kind of option, then go to the thread on rule machine. On the other hand if after reading the FAQ on custom code you decide you don’t want to do that, skip to the next section.
And the rule machine topic where you will find the code that you will copy.
After doing the one time install of rule machine, you’ll be able to access rule creation screens like the following from inside the SmartThings mobile app:
Third Party Rules Engines with intuitive visual interfaces and easy installs
There are a couple of third-party rule engines which install pretty much like any app from an app store. Very popular. These are for people who don’t necessarily think like programmers, and use visual interfaces where you make a choice from drop down Lists for each rule. So you don’t have to count the number of parentheses, and you’re not likely to make a logic mistake when you’re setting up a rule.
You’ll find those discussed in the following thread:
After installing those, you’ll create rules using screens that typically look like this:
So less powerful than Rule Machine, but sufficient for many people.
Routines, Smart Lights, and other Official Options
SmartThings itself does have a number of built-in scheduler options, it’s just that they’re not really presented in a very intuitive way. The following topic is an overview of many of these, with links to more details. If you want to really explore the various ways of setting up controls in SmartThings, this is a good place to start.