Certified Associate Developer exam

When I was new (a long time ago now) I would spend a little bit of my free time just figuring out how to get expression rules to do what I wanted them to do - or sometimes, seeing someone ask a question here and seeing if I could build my own solution to it.  I'd just keep a browser tab open to the Appian Functions documentation page and flip through, figuring out ways in which I'd use a particular function, and/or trying one in an expression rule and making sure I understand what it does and how it works.

And as always I should point out: make sure you've completed the available online trainings Appian offers - they cover a lot of this stuff, if a little bit briefly from what I've seen.  From there, you should try creating your own small test sites / applications / actions, just to make sure you know how to.

As Mike suggested going through Appian trainings helps a lot. We also have Practice test available at the end of trainings to understand the pattern of questions being asked.

We do a lot in expression rules other than using functions, simple to complex requirements.

I usually take a scenario and try to apply all available functions on it.
For example, we have lot of looping functions available and one is always better over the other. I always apply scenario with various looping functions and find out the challenges, performance, limitations of each when applied. So i know when to use what and why.

For SDLC, along with Appian resources look for resource from google. We have tons of information on SDLC.

You can refer to this blog from Kunal - https://kunalsharda.com/2021/06/18/appian-certification-program/
This should give you a clear idea and all the resources as well.