It's probably best to approach every painting day anew, with a renewed spirit and without attachment to what you did the day before.
In the morning, I try to avoid glancing at my painting from the day before. Too great a chance of seeing something that now bothers me, or of thinking, "How will I do better today?" Instead I go forward with a blank mind that is open just to now—to how a place or a motif makes me feel now. I keep in mind a refrain of Maya Angelou's: "You must invent yourself, each day." Each day, each moment, is new, and you can help yourself serve the opportunities it presents by opening yourself to its uniqueness.
With art, it's vitally important to stay open, particularly if you've set yourself the task of learning from doing rather than from studying others' work. In the field, you need to keep your eyes and other senses open because the light and other conditions are always distinct: you can't fall back on memory, history, past assumptions, even past interpretations. You're a different artist each day. Since yesterday, you may have gotten less sleep, changed your mood, learned new information, etc. You will see differently today, and so you need to paint differently. Let yourself. Push into the future.
A trap is to find yourself thinking: I can't do THAT (paint that way, use paint that way, take on that subject): I haven't done that before, it might not work, my style won't adapt to that, my (imagined) audience wants to see consistency, etc. Don't fall in that trap. Jump out of your own box every day. It's the best way to grow, to discover new things and new capabilities. Also: it's a great way to conquer fear, which will always be your worst enemy.
