• Keep equipment as simple and portable as possible – you may have to carry it a long way.
• When you find a view that interests and inspires you, go for it! Don't be tempted to see what's round the next corner, you could end up walking miles and getting so tired and frustrated that you lose the appetite to do anything.
• On a sunny day, try to position yourself so that you are in the shade to avoid glare from the white paper. If this is not possible sunglasses are an option, but remember that you'll need to keep them on throughout the painting process.
• Use a card viewfinder to isolate your composition and decide on the format: landscape, portrait or square.
• Squinting through half-closed eyes will simplify scenes and enhance the tonal range.
• If possible, divide your palette into warm and cool colours. This makes mixing more logical and effective.
• The option of standing at an easel gives you the advantage of a higher viewpoint – useful for looking over low walls, for example.
• To encourage a freer, looser style, set yourself a time limit of (say) one hour. The shadows and light will probably have changed in this amount of time anyway.
• Early morning and late afternoon provide the more interesting light effects. Avoid midday when the sun is at its highest. Try working contre-jour (into the light): this simplifies detail and makes for a more dramatic atmosphere.
• When you have settled on your view, concentrate on first painting the elements that might change: figures, boats, cars, shadows etc. Buildings and trees will not move

DEMONSTRATION: Dunster Castle

In this painting I wanted to capture the dappled light and the texture and form of the trees, and to try to convey the warmth and brightness of a sunny day by the use of strong shadows.

STAGE ONE

I carefully drew the picture out on to a sheet of stretched Bockingford 300gsm. At this stage I was undecided about the inclusion of the central figures

STAGE TWO

I quickly dropped in a wet-into-wet sky and proceeded to block in the initial greens, mixing ultramarine and cobalt blue with cadmium, lemon yellow and raw sienna to get a variety of tone and temperature

STAGE THREE

I worked up the castle, blocked in the un-shaded trunk of the main tree and started to work in some of the detail of the foliage. I also decided that two figures would add a focus and indication of scale

FINISHED PAINTING

Dunster Castle, watercolour, (28x38cm)

This was the stage where I hoped the picture would come to life! I added the dark shadows throughout, using a bold mix of ultramarine and alizarin crimson for the shadows on the palm trees. I left bits out of the washes and cut round foliage shapes to create the dappled light effects I was after. This does involve drawing with a big brush (No. 12) which has a really good point. Finally, I scratched out some branches on the left that were catching the light, using a sharp blade.

Discover plein air painting in Gozo with this demonstration by Thalia Stones

Read top tips for painting at National Trust properties from Tony Underhill

Enjoy Mark Buck's experiences of plein air painting at the Ffestiniog Railway.