For me, Corp decks are about a plan for winning and what that looks like, usually around the strength of a certain combo of cards. I really like poor choice situations for the runner, and work towards the best way to set them up.
Starting with your agenda plan is often a good idea, and it helps inform your mix. Is your plan to score out? Fast advance, never advance, always advance? Flatline?
Do you plan traps? They should match your agenda plan so one looks like the other and vice versa. Junebugs stick out in a never advance plan, but Mumbad Virtual Tour plays the same as agendas.
If your primary line of play is countered, what is the backup plan? What is your economy plan, and does it meet the needs of your primary and alternate win condition?
Ice needs be worked out. Are you rushing or need to protect early cards? Make sure you have a good selection of ETR ice you can rez fairly inexpensively. Taxing ice is helpful in the long game. Pay attention to have a balance of types, number of subs, strengths, and rez cost. None of that is set in stone, but being aware of it can help identify weak points. For example, too much costly ice can cripple you.
After the basics of agendas, win condition, econ, and ice, you might have room for some tech cards. Sprinkle for flavor and watch for opportunities to fill gaps in your plan and mitigate vulnerabilities.
This is all really basic, but you have to start somewhere.