"The game starts at 6:30 pm, but anybody who needs to level up or buy stuff for their character should come a little early."
Part of the fun is leveling up and buying stuff for your character. Many RPGs, especially D&D, are about accumulation. In pre-3e versions of D&D, your character often got more experience points from treasure than from defeating monsters. In the post-3e world that's changed (unless you're playing those older versions or a retroclone). Even more "modern" games have shifted their focus, giving characters a each a broad array of skills and abilities, in order for a player to perfectly customize his or her character.
Some call this min/maxing. Others call it character building or optimization.
I call it a potential waste of game time.
The essence of this series, Victoria Praeparatio Amat, is that what makes or breaks a great session is what happens before the game starts. Having your character done before session starts goes a long way.You've done your prep work. You're not that guy who mulls over every ability and modifier while other players patiently wait for the game to begin.
Now most sessions will have about 15-30 minutes of small talk at the beginning before actual play begins.
Aside from a few small calculations and scribblings here and there, that isn't the time to start fully min-maxing your character. That's the time to get relaxed, discuss things, and get ready to play.
An old DM trick I've used is to announce that the session starts at a given time, usually have hour before I really want the session to actually begin. For example, if I say the game will begin at 6:30 pm. I really don't plan actually running the game until around 7 pm.
This gives a cushion of time to allow for people settling in, doing last-minute updates to their character, and to allow for late arrivals.
If you use this trick, don't let your players find out. (Hell, maybe I shouldn't have posted this in case my players read it).
Overall, have you character sheet organized and ready to play before the session begins.
(Okay, I admit, this might have been a "Well, duh!" kind of post for VPA, but it still amazes me how even veteran players will wait until the last minute to update their character sheets).