I would start with the torso; search 'torso', then filter by colour (remember the arms may be a different colour, so ignore these for now). Obviously there will be lots of the most common colours, so you can use filters (male/female) or keywords ('badge', 'pocket', etc), but sometimes it's not a quick or straightforward process. Websites like goatleg.com and avbricks.no can help, but are skewed towards BL, although I think goatleg is now more integrated with BO's catalogue.
I tend to google either just the legs or just the torso as usually they will have some kind of distinguising mark or colour. Once you have a match, (I find that bricklink tends to be most successful) you can then click into it and it will tell you which figure that part comes from. Alternatively if its something that I am really really struggling with I will just post a picture on the forums here and so far I have not had a figure that somebody has not been able to identify.
I usually start with the torso and/or legs as well. As soon as I've found the torso I continue with "comes in" and then you usually get the complete possibilities of minifigures with that particular item. Final step is to check wether I have all the items (head, torso, legs, hat/hair, accessories) to complete the minifigure before it goes on sale.
So far only one mistake (wrong head) made in a year and a half sales.
I use a free website (made by a friend) called https://figureitout.app/ it finds the part(s) on Bricklink and then I look at what set it comes from and look it up on Brickowl....
You can also search this forum for hints... older threads have also suggested other web sites that can help you with your search also. We all go through this. Good luck! :-)
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So far only one mistake (wrong head) made in a year and a half sales.