US Master's Swimming has a great program called Go The Distance. The point is to have a measurable fitness goal that you can track. Since I'm not a USMS member, I don't have access to the online calculator but they have a nifty spreadsheet that I've been using.
With this spreadsheet, I set a goal of 12 miles for December and am proud to say I only have a third of a mile left in the next two days. I'm thinking about splitting it up into two 300 yard days or possibly even EXCEEDING my goal.
I'm not a big fan of upping my goals dramatically day by day, but a solid goal of 12.5 miles in January is very achievable. That is basically 1100 yards per day for 20 days. February has the same 20 weekdays, so I'm thinking of going for 1200 yards per day and getting to a bit over 13.5 miles by then. At that point, I'll be so darned fit I'll never have to swim another day in my life and may just give up the sport.
But until then I have my December goal. I plan on letting out a big whoop when I finish my 24th lap tomorrow.