The NOT fun way: watch videos about color theory and study your favourite rendered pieces from your favourite artists.
The fun way: watch 1 (one) video about color theory -> draw -> anguish about your skills -> study again -> draw but a bit better than before -> anguish again -> leave art for a week -> "Hey I'm getting pretty good at this."
ChronoNG
I'd say make sure to stick to a pallet, don't have super bright and harsh colors mixed with super soft and pastel colors.