The helper in your phone shows you what to do next
The most important steps you need to do until you can kill someone are this:
1. Talk to Davide and Bruce at 20:00pm outside of the house (agree to help them)
2. Talk to Davide again at 21:00pm in the livingroom (agree to help Davide with the drug boxes) You can only get one box each day and only at this time
3. Deliver the first drug box to the subway station at 7:00am and 8:00am (only available on Tuesday and Thursday)
4. Get the second drugbox from davide again at 21:00pm in the livingroom by agreeing to help him again
5. Deliver the second drug box to the subway station at 7:00am and 8:00am again (Make sure it's Tuesday or Thursday again)
After you have done all this, talk to Davide at 21:00pm in the livingroom again and a scene will lead you to go to the basement with him.
After this event, you'll become a FULL gang member and this is required for having access in the basement and to sell drugs in the basement at 16:00pm daily, and the kitchen event at 09:00am for cassandra. She will ask you if you let her join or wait.
Then it is required to do the weekend dates for each girl (first and second date) especially nicole you need $200 for to unlock the first date. You need to be a FULL gang member to unlock her second date (Love or Corruption second date doesn't matter, you need to do one of the second dates at least once depending on which route).
You can only do the outing cassandra in the CORRUPTION PATH to show the other gang members that she is your girl only AFTER you have done the outing with Nicole otherwise it will fail (or if you have SAZ mod installed you can do it in the love route as well) but this is not necessary to push the story if you don't want to corrupt her in the original game.
There are events placed in your room that you can start them only from there. The kill option(s) will be available in your room so check your room as well