I was a maid in a maid cafe at Youmacon for 2 years.
1. The better your people skills, the more fun it is for everybody. They don't really want your crappy tea and snacks that they can probably find better versions of in their own hotel room - they want to talk to the maids.
2. You don't have to talk in a silly high voice, which some girls did.... why? ....maybe they thought it was cute or they thought they had to? This is not required so if you feel silly mimicking ~KaWaiiDeSuuuU~ voices, then don't. However, if you think that's fun, go for it.
3. Don't expect tips. I know, sad.
I was also a waitress IRL for about 2 years, so here are the differences between waitresses and maid cafe girls:
IRL, speedy service and accuracy is important. You aren't expected to chit chat, you aren't expected to look good, you give them their order as quick as possible, are polite, and stay out of the way.
At the maid cafe, looks and personality are important. You are expected to be engaging, bubbly, and chatty. Speed can come secondary to that.
My first year at Youmacon I spent the first shift rushing around like a usual waitress trying to get everyone everything on time like I normally would, not chatting much. Once I realized NO ONE TIPPED ANYWAY, I became much more relaxed with my speed and just quizzed my tables on what panels they liked, what guests they were excited about, etc.
All in all, they don't want food and drinks, they want interaction with the maids. You can be a crappy "waitress" but still be a great cafe maid.