I have been playing poker professionally for nearly 5 years now. I have found a system that consistently profits. Once you reach this level it can be difficult to remain profitable over the long run. Online poker can have great streaks.
The first and most important step is to take notes. Use a spreadsheet. Write down everything. Write down your time, bankroll and end result for each table played at. Why you won, or why you lost. Also note the casino site if you play at several. Never stop taking notes. I have notes going back for several years. I have found that playing at lower stakes tables is more profitable (which is obvious, as the players are usually less experienced. Less obvious information I found is that certain sites are more profitable for me. Some sites promote more and have new players, which is great for you. I talk about this more on my website. So always take notes and always learn from them
The second step to remaining profitable is to stay consistent. If you win a few big games and are up DO NOT jump to a higher stakes table and throw your entire bankroll into a larger game. I gradually step my game up to higher stakes tables over years. There is more money at these tables to make but the players are much better. You can use your notes to find the most profitable table for you. If you play at a higher stakes table you will make more money but it will take longer so you will make less over the long run. The key is to find the perfect table to suit you. As you become better and more experienced gradually move to higher tables and note the changes.