Petting and excitement

Question
Hi there.  I have a 1 year old fixed Female Chocolate Lab named Mouse.

I always make her sit when I go to pet her.  However, when I start she continually stands and tries to rub against you (picture a cat rubbing against your leg).  I say no, stop petting her and make her sit again and start over.  However, this does not seem to be working at all.

Also when people come over I make her sit before opening the door.  Make her wait until I give her permission to greet them.  But she gets all bouncy,(even when I holding her collar) tries to rub against them.  making it impossible for them to pet her civily.  Any suggestions as I am trying everything i have read on the site to no avail.

Thanks for your help

Answer
This is a difficult one.  One big difference between better dog trainers and others is self discipline.  I fail at this myself.  When I came down stairs this morning, I had 3 Labs dancing on the other side of the gate we use to keep dogs in the other room.  I pushed my way through the gate and petted them.  

You need to be very consistent about not petting them unless they are quiet and asking others to do the same.  Even petting an excited dog once in a while will undo your efforts.  It takes time and plenty of will power.