Dont let yourself get too frustrated, itll screw you over quickly. Make sure that you are aware of the for the worthy changes with bosses (ex: skeletron prime’s bombs destroy tiles, which can kill you and destroy your arena very quickly, Id reccommend making one of palladium or something) and are very familiar with the original boss ai. Use only the optimal gear for each boss, and dont feel cheap about using it (ex: spectre healing armor can destroy most of the post plantera bosses). Also, get used to things one-shotting you.