I agree with some stuff said by other users.
About the ult, only use it when there is a play to be made. It's a super long cool down and you can only use it at the right time. On top of that everytime you do use it, you are putting your opponent laner ahead. It's important to catch up in farm.
Know what your W can block. It can block any auto(duh) but also enhanced autos(nasus q and even Garen q) and three hit passive procs like gnars magic damage and vaynes true damage. It's also possible to block Warwicks ult (lol) see him dive you with R? Click W.
Also get Tiamat for waveclear into Titanic Hydra, honestly Sunfire cape is trash, I still wonder why I build it when Hydra is a superior waveclear item and actually adds to your damage output towards champions.
Also hop over to r/ Shen for more info(subreddit for Shen mains)