My main issues being, as a runner, not to know what to do, and as the corp, feeling really insecure all the time.Thanks!
The articles on this very site would be a good place to start:
If you prefer, just look at the ones categorised as articles for newer players to start off with.
I think there's at least two articles every new netrunner players should read to understand some basic but crucial concept on this game:
http://stimhack.com/playing-the-opening/ <= The first one, wrote by Alexfrog a year and half ago is about how to play your opening both as corp and runner. https://boardgamegeek.com/blogpost/25932/matchpoint-theory-rush-hybrids <= The second one is about understanding the corp deckbuilding and the value of rush during the early game to ensure a lead.