The 2 major + some minor categories
#1 tech tips, observations, experiences —
#2 finance/trading/quant knowledge
# wall st tech workplace realities
I feel #1 is more widely useful. My #2 content is often amateurish.
Introductory topics are more widely useful, but there are often good explanations online and in print, so you may need to specialize on a niche topic. Most importantly, you need to develop a communication style to reach out to beginners, using clear English.