This is the method i use to prepare my Nordicware bundt tins. Some people use non-stick sprays but I do not like the smells, of the ones I have tried.
Melt some butter and brush the inside of your bundt tin, make sure it reaches all grooves.
Sprinkle in some flour and gently tap your bundt tin to make sure flour goes in all areas on the butters part.
If baking chocolate cakes you can try using cocoa po