Your skills and patience are one thing.
The games you choose to play, make up a huge percentage of your success.
Sit and goes are great to make a small long term profit. Double up games are good too. The problem is that these games get boring after awhile because they are for a better word (lack the excitement). I do my best at playing in private games with money added. There are lots to choose from on a daily basis. You just got to look for them. When I played a 100 sit and goes a week, I averaged $100 profit a month. I quit playing sit and goes now and spend my free time on NDN forum and play added money games and now averaging $200 a month. Stay away from cash games and re-buy games.
Good examples of good games to play: $1 entry $50 added 17 players.
$2 entry $100 added 40 players. I played in both this week and there are 2 more this week.

Summary: stay active at NDN, choose your games wisely and make a profit.