First Impressions

If you work in any area of service you know how important your appearance, demeanor, and body language is to give the right impression to your guests.  Being a tipped employee, such as a server, delivery person, bartender, etc., you know how much more crucial this impression is since it has a direct effect on your wallet.
Here are some tips:

a. Always make eye contact whenever, and to whomever, you are speaking to.
b. Smile.  Genuine smiles make the guest know you are truly intending on making sure their visit is amazing.
c. If they are regulars, or if you've seen them there before... mention it.  Shows that you pay attention even if you weren't the one taking care of them before.  Thus, they know they will be well taken care of.
d. Dress appropriately for the position.  Being a server doesn't require a hairnet, but if your hair touches your shoulders, it should be pulled up and contained properly. 
e. There's nothing wrong with a well-kept goatee or mustache, just as long as the remaining area is clean shaven.  This is all about hygiene. 
f. Speaking of hygiene... clean fingernails, no body odor or heaving perfumes (both are equally bad), appropriate amount of make-up(no emos), minimum on the jewelry(and yes this includes earrings), and definitely tuck in your shirt if it was meant to!
g. If your guest is not happy with something (anything even if it has nothing to do with you)... apologize and inform the manager on duty.
h. Always ensure guest glasses are atleast half full.  Unless it's alcohol, you should automatically be getting them a refill.
i. Water is expected when alcohol or coffee is ordered.  A lot of restaurants automatically server water, I am a full supporter of this, but in those cases where it is not a part of their server expectations, always offer because we expect it.
j.  Even if you shift is about to end, you've done all your side work and your waiting on that one last table.... Do Not Hover or Hand Them Off. 
k. Smile and acknowledge all guests, not just yours.  Next time they may be your guests.
l.  Never complain to your guests about anything.
m. Pay attention to all the guests at the table.  There's nothing worse than a female server giving the man all the eye contact or attention.  Most of the time, it's the woman who decides your tip!!!  Vice versa for guys!
n.  Never let them see you sweat.  I know how hard this can be as hot as kitchens get, but there's nothing wrong with using a beverage napkin to wipe off any visible presperation.
o.  Don't mingle with other servers on the floor.  Nine times out of ten the guests can hear you.
p.  When clearly un-necessary glasses never use the claw method (fingers in glasses) to remove them.  This is a serious food safety issue.
q.  Wash your hands frequently.  Though you may not have to handle food directly, you do clear dishes and cups that could be carrying germs.
r.  No gum chewing.  This is just disgusting to guests.   No "Flo's" allowed in this day and age.
s.  Keep your apron clean.  Your guests will wondering how many times you wiped your hands on the apron versus washing them.
t.  Always be respectful of your manager.  How well you keep your cool in tough situations will benefit you and your wallet.
u.  Be ready when you walk in the door.  No guest wants to wait for you to touch up your make-up in the bathroom before they get service.
v.  Read your guests facial expressions and body language.  This is a way of being pro-active to possible tough situations you can remedy before it gets worse.
w.  Don't count your tips or money in guest view.  Personally, I say don't count until your shift is completely over.  If your focus is on the money and not on the guest it will show in total tips.
x.  Always offer dessert.  Even if they didn't finish their entrees you never know if they were saving room especially for that big vanilla bean cheesecake they saw as they walked by another table.
y.  Never sit with your guests if you have other tables.  Doing this shows your other tables that you are too distracted.  If you talk with regulars.. make it brief and always remain standing.
z.  Don't be greedy with the tables.  Having more tables does not bring you more tips.  Better service does, so focus on what you've got and make it the best visit they've ever had!!!