Jean likes to experiment in his sketchbooks. Remember, don't get overly attached to sketchbook drawings: within a year you'll be twice as good and all your old drawings will be stored somewhere. Don't be afraid to overlap, continue from one unrelated object to another, paint over old drawings, etc. Loosen up!
Draw your surroundings, even if you think they're boring! Many brilliant sketchbook drawings and famous paintings were done in common, everyday places. Take your sketchbook and a pencil/pen EVERYWHERE!