Even five minutes of daily sketching can get your skill pretty far. It's a way to wire your brain to move your hand how you want it to move. Practice strokes, capture proportions, and decode perspective. It doesn't need to be a big effort as long as you do it every single day. What's key is to enjoy it so those five minutes flow into a longer drawing session when you have time.
Needless to say, you can apply this logic to activities other than sketching that you enjoy doing. I use it daily for sketching and writing.
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