I often get asked about plein air painting (painting on site or painting outdoors).  Although it is not my choice of painting ( I would rather paint indoors), it can be a very rewarding experience.  Plein air painting with watercolor does present some additional concerns.  First, your paint will dry much quicker outdoors especially during midday.  If you bring along a water, spray bottle you can spritz your painting as needed.   And there may be more distractions outdoors.  The better you are prepared with your materials and subject matter the more focused you will be.  Also, it may be the time to work more simplified than usual:  smaller paper, fewer paints and brushes, and a less congested area.  There are many groups that gather to paint outdoors.  This may be the best way to start and pick up additional tips from others.