Categorizing Opponents: Method of Sizing up a Table?

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Sometimes I have the comfort of playing against local regulars, but often I'm confronted by unknowns. I'm looking for a technique to aid me in categorizing my opponents in B&M games. The ineffective way I do it now is to observe the early action when I join the table and see who seems dangerous. This leads to me obsessing on the actions of 2 or 3 players and missing the threat from the other seats.

My tiny brain needs a filing system to handle the behaviors and betting patterns of nine other players. I'm sure some people are naturals at organizing this data, but I have to work at it. Any suggestions or reading recommendations for help would be greatly appreciated