For me personally, I set monthly goals and have done for a while now. Recently I have set myself a yearly goal (July 2014 to reach it).
Monthly is based on what I have achieved in the past (percentage increase in income each month). The idea of my monthly is to make it a realistic goal and at the same time a goal that requires work to achieve.
For my yearly, it is basically to reach a certain amount of revenue per month by July 2014 along with a few other bits and pieces - nothing to do with percentages (the monthly percentage gains lead to the yearly goal).
Then I have a few rules for myself to reach these goals.
Stay consistent.
Don't try and do too much (ie don't spread myself too thin).
Don't let a few bad days of sales put me off track (look at things in a monthly / overall manner rather than day to day / second to second).
Do not over work myself, take time off when needed, exercise regularly, see friends & family - believe me this is the most important part.
When I first started setting goals, I was basically just making shit up as I had no clue what was I could realistically achieve. So my advice is to record the data you currently have for 2 or 3 months, see what you can achieve and set goals based on this. Then keep track of what you are doing to increase revenue - figure out what works.
Once you start tracking things, setting goals that you can realistically achieve becomes far easier. Then you can set a few goals that are maybe a little out of reach
Defining success for me is to increase revenue each month. However if I reach my percentage gain per month, I reward myself with something - nothing huge - a day off, buy something, go out / big drink up / massive feast etc...
Hope that is of some help - I am by no means anytype of player and struggle through like anyone, just found setting goals a great way to get all my ducks in a row.
Good luck.