If you solo farm you should be making 10k/hour or so, much more than that do not talk about it as it will be nerfed, any less and you need a better spot (assuming your main goal is gold - I have places that make 6k/hour but give me a much higher xp/hour for skill hunters that still need skill points). 10-15k has seemed to always be where Anet wants to the farmers to stay.
Almost any decent hard mode place will give you that and every class in the game has a few spots that can do it. Peruse either PvXWiki's farming builds or (IMO better, though less organized) farming forums on this site.
Next, farm. It doesn't take much - lets say you just farm 15 minutes a day. Even very casual players can do so, when I'm looking to increase my funds I do one farming run when I start a gaming session and one when I end. If I choose them well that is a 10-20 minute commitment. With 15 minutes a day that means you will make 25k in 10 days, 50k if you can go the full 30 minutes (remember, you just need to *average* this amount of time - an hour every other day is the same as 30 minutes a day). As such it doesn't take but a few months to get into the multi-hundred platinum range.
Add in treasure chest in Nightfall (the ones you do not need keys - a full clearing of them is 30+k your first go, though it degrades each with each chest opened so try and stay in the higher end ones), trading in quest rewards for their maximum value, and just playing the game and it isn't that hard. If you really want gold for the higher end items then you move into power trading but you will have to talk to someone else about that.
Of course, the real secret is not spending it. It is easier to spend 20k/hour than it is to make 10k/hour. Set yourself goals and follow them. *Only* purchase necessities if you are below a certain level of funding (and do not rationalize it, you know if it is a necessity or not). Once you go over that level *then* decide if you really want said items or not - more often than not you not only find you could live without them quite well but you want something else. This is where the vast majority of people fail.
Personally I like about 200k in the bank along with putting whatever crafting materials I happen to find and can fit into the crafting storage (excess goes to the trader) - once I decided on that number I reached it in about a month to 1.5 months of just normal playing (farm some, play some, trade some, etc). I have not gone above 250k in the year since then and am currently sitting at 197k
