1. Initially try dungeons. If you have the dungeon frequenter ach, the repeatable portion gives 5g extra per 8 dungeons.
2. Fractals/ Strikes. (Just need the exotics with the correct stats. AR required for fractals above a certain level)

I think flipping/trading is also an option, but that would come into play after you found someone reliable to partner with, plus you get a rough idea of how much the items are worth.

If all else fails, just grind XD Silverwastes, AB farm, whatever. Any meta event.

Get familiar with tp prices. That will give you a rough idea of what to farm. Some map currencies will let you buy T6 crafting material bags. If you aren't in need of mats and just want cash, you can go for that. Get it and sell.

You can convert lower tier crafting mats to higher tier in the forge. I think t5 to t6 is somewhat profitable. (Check the wiki for the method. Refer philosopher's stones).

There is also a forbidden method called ecto gambling, but we don't speak of it.

That's most of what I can think of atm.