Breaker box that is full
Assuming that there are no service capacity constraints, you have a few options:


Replace some of the breakers with tandem breakers.  These essentially double the density of each slot.  These breakers come in a variety of configurations of both 120/240V and combos with both.  This is the easiest of options for a do-it-yourselfer to complete.
Install a sub-panel. You would relocate a number of circuits from the current box to a new sub-panel.
Replace the entire breaker panel with a larger panel. This is the most difficult of the three options and sometimes requires the utility to disconnect your service in order to complete this.


As always, contact a licensed electrician if you are unsure of how to safely make these modifications.