Welcome! 
There’s no one best way to do anything because different households have different requirements and preferences. For example, someone who lives alone would probably really like lights to turn on and off as they move around the house. But if you have two kids and a dog that’s not likely to work as well for you. So it always comes down to the small details, but you’ll find lots of people in the community who will be glad to help you.
The most significant changes since 2015 are First the introduction of two new official features, smart lighting and smart home monitor, which can both do a lot of automations that used to require individual focused Smartapps.
And then some very significant community – created offerings. There are now two major voice assistant smart apps, askAlexa and EchoSistant, both of which can do amazing things with Amazon devices. (You’ll find these on the voice lists in the community – created wiki mentioned below)
And then the introduction of first core and then webcore, which are essentially scripting languages for smartthings and allow you to create much more complex rules than the official features. So now, the answer to many “how do I automate…?” Questions is just “webcore.”
Another community feature that was added in the last year or so is the community – created wiki. There’s a lot of great information there, including the “quick browse lists” which should let you very quickly find both project reports and custom code contributed by other community members. These are divided by topic like “mailbox projects,” “irrigation projects,” etc. so that’s definitely a good place to check. There’s also a quick browse list under Project Reports called “get started” which has all kinds of topics from “top 10 things to do with SmartThings” to “what device should I get next?” Lots of great stuff there, both fun and practical.
Finally, when it comes to specific device questions, start with the device feature FAQ:
If you don’t see the device class there that you’re interested in, such as sprinklers, feel free to start a new thread under the devices category of the form. Please limit each thread to just one device class, or it becomes impossible for people to go back later and find information. So one thread for sprinklers, and a different thread for car transmitters. It just keeps the topics easier to follow.
If you have questions which aren’t really about a specific device class, but are more brainstorming how to solve a particular problem when you haven’t decided on which devices to use or when you are trying to tie together multiple kinds of devices or anything which is going to be specific to you rather than something that could be answered by reading a spec sheet, then start a thread under the projects section of the forum. For example “we have a family member who is deaf, and I’m curious about what other people with similar challenges have at it in terms of home automation” or “I’m really excited about home automation and I want to do as much as I can for $2000, what would you suggest for that budget?” Or " we have a garage apartment that we rent for Airbnb, I’m curious if anyone else is adding home automation to an Airbnb suite in their home?" would all fit well under projects. The answers are likely to vary from one person to another, the solutions will probably involve multiple device classes, and a lot of it may just be community brainstorming. 
Welcome again! SmartThings is a very powerful, very flexible platform, but not easily discoverable. So you do you sometimes have to do quite a bit of research to figure out what will be the best solution for you. 