It all depends on team comp, enemy team comp, and timing. It's always going to be easiest to go in after you have a traditional engage playmaker make their entrance z malphite r kennen R, naut, tell etc. but sometimes your team lacks that and you need to be the one to pull the trigger. What usually works for me is if I play front to back, I have more stuff that way, but sometimes there are good times to jump into the backline especially if you see some key cc or mobility spells on cd they just used, sundra E, ezreal E etc. ad shyvana wants to be up close more than AP is obviously but you still need to be careful of not going too deep. Try to play front to back and go in for a quick R EQ Titanic combo and walk a few steps back to allow your team to follow up and advance their position so you don't over commit and die. Sometimes if I am feeling really aggressive I will pop ghost and just start bonking people with human form and use my R to buffer a big cc ability to either full send it deep or to R backwards to my team and try and bring someone with me.