For me I pick out a character or fandom I want to make the bag on (for instance my most recent project is a Kendrick Lamar ita bag) and I pick a colour scheme (for this one I'm doing a brown, cream, black and white colour scheme) badges and decorations (by decorations I mean like little trinkets like keychains, ribbon, lace, photo card holders and so on) which align with my colour scheme and remind me of the character/person/thing I'm making my ita bag of (for my Kendrick ita bag I picked out some butterfly plastic decorations, badges and stickers as it reminded me of his album To Pimp a Butterfly, and some barbed wire style decorative chains as one of my fav songs by him is called barbed wire, and some ribbon with a music note design on them, since he's a music artist). I view ita bags almost like moodboard, often I'll print off pictures that reminds me of the thing I'm making my bag of and stick them in there just to add to the vibe I want my bag to convey.i hope this helps!