1. have a Jawa Juice
(it can be as dull as flat water or whatever you like)
2. Know what you like
Set yourself a modest and specific goal (such as: "that armor is ugly, I have to replace it!" or "every toon has to look like Bastila or Carth!"): in other words, something you can see the end of such as recoloring, retexturing, changing something very specific in the game or adding an item to begin with and you'll be good. It will allow you to learn a few aspects of modding and how the game files structure work.
I started modding because my old computer back in 2003 could barely handle swoop races...I had to find a way to win! I didn't know anything about modding so one day I explored the game and its files, found the first version of kotor tool which was only a few months (if not a few weeks) old on LF, experimented like a mad scientist (i had no clue as to what I was doing) and found a workaround the swoop nightmare. Nowadays there are many tutorials but if you can't find what you are looking for, move to item 5.
4. Don't get lost
Don't start with an ambitious conversion project that you'll never see the end of.
5. Ask questions
What you think might be a stupid question> not asking and being stuck
6. Have fun
(no explanation needed)