Don't try playing harder content if you don't know how they work. Forums are specially made for people to come over and discuss, ask for help, search guild. I have been like you, but theorising NiM tacts weren't enough finish SnV. Nowadays guilds have two types: progression which demand high skill and knowledge and social/chill raiding guilds who take everything much slower, eventually playing HM ops few weeks later. Search for guild who operates in mastering SM (not like casual run, but trying different classes combo's and finding urself that fits ur gameplay) and doing or atleast preparing ppl to do HM. This way you will not only get better realisation of endgame experience but also know ur role better. Endgame is not only about operations, flashpoints, gear and titles. Calling yourself experienced isn't what is supposed to be important. If have no class experience or it's only basic but u do have HM/NiM achievs, this doesn't mean ur very experience or any good. Want to become better? Use classes guides, important positions, team callouts and make short plan in which you mark all the movements u will make and tacts u will use.