Here are my top 10 tips when painting outdoors.  There are a lot of things to consider, but if you have a few of these in your game plan, painting outdoors will be more enjoyable, productive and memorable.

1. Pack light! –  Depending on where you are going, if you are going to be carrying your gear, you have to pack light and right!  Make sure you have a light snack, water or Gatorade.  Have a handy backpack to carry your paint, mixing palette and canvas.  Bring 2-5 brushes, 1 palette knife, paper towel. ( you can opt to take about 4-5 towel strips and fold them so they do not take space).  Stick to a basic colour palette, and perhaps bring only ½ tubes of paint, so they are not too heavy.  To see what I bring, please visit my YouTube video here.
2. Use a view finder - The landscape or scene can overwhelm you.  But if you can use a view finder, you can crop the scene into a manageable composition.
3. Location – Make sure you know where you are in your landscape.  Check where you are standing or sitting, make sure the sun won’t be in front of you after an hour into painting.  Check to see if you are in a shaded area, or if you need to bring an umbrella to tone down the brightness of the day.  Most importantly, make sure you are in a safe location, both from environment (e.g., ant hills, or secluded parts).  – I had to move a few times, when I realized, I was standing on a red ant hill!!
4. Establish your outline first – make sure you have a good drawing and composition to start with.  Light will change fast, so get your big shapes in first.  Do not go into the details until the 2^nd hour.  Start with darker values first, and use water (acrylics) or mineral spirits ( oil) to get when set up.  They will dry quickly, so you can go to the blocking in colour after. 
5. Tone your canvas – I usually tone my canvas with a light red wash.  It harmonizes the painting immediately, so if you run out of time, the underpainting can show through and can provide and overall unity.
6. Step back often - Try to step back every 5-10 minutes.  This helps you look at your scene and canvas in a different perspective. Sometimes, I take a picture with my iPhone, because this gives me a better idea of what I need to do next.  From a distance, it can give you a macro-perspective of the landscape and at the same time, allows you to rest your eyes.
7. Limit brushstrokes - Try to limit your brushstrokes and blending.  When painting outdoors, this is usually wet on wet, and if you are using oil, the brush can pick up colour that was there before the next.  This could lead to muddy colours or could stop the spontaneity of the painting.  Try to leave the brush stroke alone if you can.
8. Atmosphere – Remember that the farther the object, the more it is lighter and muted in colour.  Usually distance bring out cooler shades, so make sure you squint your eyes to see where the farthest object is in your field of vision and that will be cooler in tonal values.
9. Health and Safety – Always bring a little first aid kit, band aid, toilet paper, wet ones, hat for shade, suntan lotion and bug spray.  If possible, paint with a friend.  (or man’s best friend, like your dog).  Always good to have a buddy with you.
10. Have FUN!  Enjoy the process.  Remember, this is an exercise to improve your overall studio practice.  It is not a mission to have a masterpiece done.  It is all about observation, improving your skills, enjoying the day and being one with nature!