As said, plan for the rainy day.
Seasonal fluctuation are to be expected, barring a storm, holidays will be slower. Going toward April 15th, the people with the cash for treework will be writing a check the IRS. Back to school time seemed to be a slow time.
I've had some customers that have said to call them when I am slow. Having a few of those can help keep the stress level down when the phones stop ringing.
Work free advertising. Its free.
If you do storm damage work, start with your own agent, letting him/her know that you can do a good job at a good price. They may have other agents that will call as well when the storms hit.
Don't be shy about self-promotion.
Make sure that your employees know about fluctuations. I try to stock up some jobs that can be done on a slow week, like cutting and splitting firewood left over at the shop from jobs that require hauloff. Take those slower days for a little training.
Keep in mind the cost of overtime. Usually 1.5x's normal for over 40/ week or 80/ payperiod.
Give a small finder's fee for employees that bring in jobs. They'll keep their eyes open.
Introduce yourself to apartment complexes. Right now I'm hoping to get the job to remove a 60' dead hemlock right next to one of the buildings. The management didn't even know that it existed. Now on top of that, there building clearance and some widow makers. Property managers will sometimes report higher up to a supervisor that might also have 10 other property managers at 10 other large complexes.
Best of luck. With 4 year climbing experience, you'll have run across a lot of situations to draw from, plus you've got all of the people on the forum.