Be courteous.
Be clean including breath.
Be well dressed.
Be on time.
Don't flake on her.
Obey her boundaries.

Those are most of the musts.

Some nice to haves:

Tip.
Bring gifts.
Be a good lover, that is to say, generous.
Be witty.
Look like a Greek god

First of all, I wouldn't try too hard to be an escort's favorite client. Just be respectful of her as a provider... that means respecting both her personal boundaries, and her professional boundaries. It's a courtesy to her, and trust me, she will appreciate that. At the very least, she'll happily welcome you back (assuming that everything else went OK).

I appreciate money/tips/etc, but what really makes someone my favorite is his character and personality, and the way we relate to each other. Is he kind to me? Is he intelligent? Is he a good conversationalist? Is he compassionate? Is he easygoing? Does he have a good sense of humor? Do I have fun when I'm with him?  

(It goes without saying that he's clean, doesn't trample over my time and business, isn't rough or rude, etc.)

Some things that stress me out would be (not in any particular order): texting or emailing me to chat, not gracefully letting me leave when I start to make those 'getting ready to go' noises, forgetting that I have a personal life and trying to 'buy' me by pushing the limits of what I'm willing to offer (i.e. trying to convert me to a de-facto sugar baby).

I've known my favorites for quite some time. I trust them... they've been good to me over a period of years, and I know they don't want to date or marry me. They appreciate my service and company, and they show it by their behavior toward me (not necessarily money). For instance, I got the best relationship advice of my entire life from a 70-year-old client. He cared enough to say what he knew I needed to hear (it wasn't what I wanted to hear. But he was SO right I couldn't ignore him).  

When someone tells me flat-out that he REALLY wants to be my favorite client, I always feel like he wants to wrangle some concessions out of me... timewise, or even emotionally. It comes across as presumptuous and/or manipulative, and can actually be kind of creepy

Someone who reads my blog prior meeting me. Simple, doesn't cost money, and it helps you knowing me better. Showing interest in the intellectual side as much as the physical is such a turn on for me.  

-Show up on time.

-Come well groomed, with all hygiene items taken care of. Be ready to rewash if asked.

-Don't negotiate rates.

-Be respectful and kind.

-Respect her boundaries and limits, do not push them.

-Have fun.

-A good sense of humor goes a long way.

-Pay her how she wishes to be paid and right at first.

-Listen to her, and treat her like you care for more than her body.

-A few honest compliments go a long way.

-Read her site.

-Leave when it is time to leave, don't ask for OTC time.

-Don't be a selfish lover, but don't pressure her or require her to come. Put effort into making time with you enjoyable in and out of bed.

-Enjoy her as a woman, not just a sexual partner.

-Be honest in the screening process.

-Alway book enough time so things aren't rushed.

-Listen to her in the bed, both verbally and non-verbally.

-Don't be fake.

-Don't be a lap dog. Show respect for yourself. Don't be spineless. Don't give up your power as a customer or a man. Women do not respect jellyfish.

-Don't spam her phone/text/email. Contact her when you want to book, or leave a thank you, but limit it to that. If she wants to talk she can contact you.

-Don't be a judgemental hypocritical fool. Respect this as her job and that it a legitimate choose.

-Do remember what this relationship is. It is not a BF/GF real relationship and all commitment and responsibilities end on both parties part end after the time you paid for is up.

So in short don't be an asshole. Respect her and the nature of what this is and enjoy her as a woman and let her enjoy you as a man. Not hard really.

Don't talk bad or gossip about other humans, particularly others in the hobby.  This is a total turn off for me.

Show up sober and showered.

Be on time or let me know if you're going to be late or need to cancel.  I understand life gets in the way sometimes.

 
Looks have nothing to do with it. Money has nothing to do with it.  I don't sell my dignity and self respect and those things don't leave during a session.  If I can't first be treated with respect, no amount of money or looks will get a meeting with me.  I've never seen a gentleman so ugly I didn't want to see him.  If you look at the beauty in each person, you'll see more beauty.  A man who knows how to be a gentleman is more attractive than anyone else to me.  

I don't do anything I don't enjoy.  If I'm turned off by you, I don't see you.  I have a very rich gentleman on my "NO" list that contacts me almost every week, offering me more and more money to see him.  Money is all he has to offer and he feels he's somehow more powerful, attractive and an exception to the rules for having it.  He's confused to why I won't see him.  I won't see him because money is all he has.

 
My favorites are pretty cool guys :

especially from the ladies.  

Muchas Gracias!!

The $$ got you time with her...now what?  Be yourself, be clean, be showered, be dressed nicely.  Don't overdo the cologne (if in doubt, skip it).  If there is conversation, be interested in her and her life.  Don't judge, don't monopolize, don't brag.  Know her boundaries, and respect them.  Have a sense of humor.

Oh, and one last thing....if she allows it - good DATY FTW.  LOL.