Be kind to yourself, especially when you're struggling. This one is tough for me because I'm forever calling myself an idiot or lazy when I know I'm neither of those things. But talking down to yourself is harmful and demoralizing*. I'm really trying to practice patience with myself, and to talk to myself as kindly as I would a dear friend. And praise yourself when you do something well!
* Unless I know I'm being genuinely lazy, then a verbal kick in the pants can help ;)