Actions
The Dude chills out, drinks White Russians, and rolls joints. Walter pulls guns on innocent people. Donny drinks Orange Slice and asks too many questions. Maude Lebowski flies over a giant canvas in a harness and sprays the canvas with paint. The Big Lebowski steals money from his wife's charity to keep for himself. Bunny Lebowski runs away from home and marries an aging multimillionaire.
In this film, people's actions say a lot about who they are, perhaps more than their words. Analyzing the actions in the above paragraph, we can draw some pretty clear conclusions about all of these characters. The Dude is a peaceful (read: lazy) guy who's got some chemical vices. Walter is a trigger-happy veteran with PTSD. Donny is a child in an adult's body. Maude Lebowski is nontraditional and bold. The Big Lebowski is a liar and a sociopath. Bunny Lebowski is a naïve farm girl who's struggling to find herself. Characters behave pretty consistently in the film, so it's not hard to interpret their actions.
Clothing
Clothes make the man (and woman) in The Big Lebowski. The Dude dresses like a slob, in bathrobes and ripped t-shirts (which he wears in public), because he is a slob. And, okay, if you want to be really generous, you could also say he doesn't really care about how the world sees him, which is part of The Dude's Zen mentality about everything.
Even though Walter has returned to civilian status, he still wears camouflage vests and night vision-enhancing aviators, both relics from his time in combat. He's still operating in war mode, which explains all of his unexpected violent outbursts. Although Bunny Lebowski is a married woman, she's barely old enough to drive a car: she dresses in girlishly revealing outfits, which signals her childishness to the audience.
And Maude Lebowski, whose frankness about female sexuality is basically written in bold Sharpie all over her artwork, frequently wears nothing at all.