From working in an industry based on taste and personal preference you get to learn a few things about clients, how they work and how some of them really have no taste at all... its not their fault, we can't all be blessed with impeccable taste, some of us just can't spell, cook or tie our own shoe laces, it keeps the world a varied place.
1) Clients are always right, regardless of whether they are clearly, blatantly, indefensibly wrong, they are always, always right.
2) When it come to design, a lot of clients don't know what they want until they see what they do want! This rejection can be just as useful.
3) If something goes wrong or goes to print late, it will forever be your fault. I've learnt to put every detail in email, as you will always need to know what you said on Jan 31st at 10.24am precisely.
4) Some people have awful tastes, as a designer you can only try and guide them in the right direction. Try not to take it personally if they completely rebel against this and stick to what they want to do, you can't always win.
5) If clients give you their final decision before asking their family and friends, however much they love your work, this will never be their final decision post asking family and friends.
6) Clients are not designers. Remember you are literally talking to someone from a different planet when asking for a high resolution image or a logo as a vector .eps. They don't know, and don't really care. You find the logo, thats what I'm paying you to do, right?
7) Some clients just want what they want. However many considered concepts you show them, however much heart and soul you put into your 6 different designs, if they came in asking for a duck with a bow 'round it, they are walking out with a duck in a bow! You might be able to push them a little but I wouldn't bet on it!
8) Clients will always make the most important changes and decisions last minute, so on a night where you have a big sign off or something is going to print, cancel your dinner plans and bring a sleeping bag!
9) Some clients are picky, really really picky. Keep telling yourself it's their baby and its only because they care - humour them and get it done.
10) Clients are the most important part of business so be patient and be nicer to them than you would your Grandma! Without them, there is no business, so pucker up.