You need to learn how to design a circuit and how not to design a circuit. The best way to do that is design stuff, and find out the hard way that something doesn't work (expensive) or start looking at other designs, preferably ones that are done well (most of the stuff you'll find online are really bad to barely okay designs) and learn from people who know what they are doing. If you can't do that then get some books on circuit/digital design.
You could also browse the forum for posts from the long time members with >>1000's of posts with >>1000's helped. Many of them have given sound design advice to other queries, learn those tidbits and you'll probably be ahead of many engineers that are interviewing alongside you.