I don't want to encourage anybody ending their life, but if you are certain and set on this method, what I can say is the only reason to take alcohol or meds is for your SI. For the jumping, just make sure you're landing on hard ground, ideally concrete or tiles. Head first, or at least make sure to not lend on your feet (more likely to survive with horrible injuries).
Despite what people say, this method is highly lethal and has high success chances.
Consider any other possibilities before disappearing forever though
How high of a place? If it's high enough, you won't have to worry about being conscious and even if you were, no pain meds would help. Good luck.
To add to this, yeah, if you have access to a high enough place the type of ground or how you jump will make no difference as long as you don't hit anything on the way down.