I assume that you're asking here because you work at a small company and there isn't anyone there to ask...
(1) You are there to provide technical information don't try to turn this into a stand up routine...
Now for all the "soft" things that make a training meeting go well....
(1) You should have a 3-ring notebook with b/w copy of any presentations so that the students can make notes on slides. (3-Ring notebook should have company logo, or at least insert with company name.)
(2) At very start of class discuss what happens in event of fire drill? Where should people exit? Where to meet so that you can count noses?
(3) Where are restrooms? Any phones or computers that students can use? Where to hang up coats?
(4) What to do about lunch? If folks go out it can turn into a two hour wait easily. Bring in food if you can. If you have a lunchroom can you reserve a table so all the students can sit together?
(5) If this is a small company, can you have president stop by to say hi? or for lunch? Some other executive?
(6) Anyone else in company that students might have dealt with regularly? Have them stop and say hi. (Eg someone from software support...)
(7) If folks will be staying overnight have a list of nearby restaurants and directions. Give some idea of price for local restaurants that are not chains.
(8) If folks will be away at lunch be sure that room can be locked. If a customer has something stolen it will be a very very bad situation.
(9) Have pens, and paper available for notes.
(10) Diskettes, CDs, zip drives to take home "dummy data sets" if appropriate. (So I set up some spreadsheet to do a calc as part of the class. Let me save my work so that I can take it home...)
(11) Hard candy and bottles of water are nice for table. Pastries/Coffee in am? Sodas & cookies for pm snack at break?
(12) If folks can get some sort of continuing education points for this be sure to have some sort of certificate. (I'm a project manager, and this is a class on MS project with 3 days of class room time or 24 contact hours...)
(13) Some sort of feedback sheet on class, and facilities for feedback. (Folks may or may not give any useful answers but give them a chance. Optional to give name..)
(14) If this is a small company be sure that everyone that the students will come in contact with knows that these are customers. Everyone in your company must be using "company" manners.
(15) Tent cards for names. Badges/Name tags?
(16) Don't tie up class discussing a weird problem one customer is having. Tell customer you'll talk after class. (Eg Customer wants to dump something then format it to put it into their XYZ system. Unlikely that anyone else has XYZ.)
(17) Make firm commitment to end class on time on last day. (Folks may have plan to catch to get back home...)
(18) Do you intend to give out manuals for product? If you have a lot of stuff some sort of bag to hold all the junk. Ideal would be some sort of bag with your company's logo.
(19) If folks are coming from out of town do you have some hotel recommendation ready. Need directions from airport to hotel (or through town) and hotel to site.
(20) Don't try to do class alone. It is great to have someone else listening even if you do all the talking. It is very hard to listen and think about what to say at the same time. So second person can really help listen to customer's questions to be sure that questions get answered.
(21) Don't be afraid of asking "Did that answer your question?"
(22) No matter what happens, don't let them see you sweat. Stay calm. Very calm.
(23) Don't disparage anyone in your company about anything. It just makes you all look like a bunch of idiots. (Fred didn't get network set up for class? Ream Fred out of ear shot of student's...)
(24) Some other sort of company logo'ed trinket? Mouse-pad? Mug? Pens?
(25) Don't be afraid of saying "I don't know. I'll check and get back to you..." (Nobody knows all features of product.)
(26) Be sure screen for presentation can be placed so that all students can see it. Can room be darkened enough?
Hope this helps...