You've got the photographer booked to shoot the engagement session finally.  Now what?  As the day approaches and you both talk about what to wear, you realize he is probably somewhat nonchalant about the whole thing.  Maybe he says, "just tell me what to wear, and I'll be there".  Hopefully not, but I've seen it.  It's not necessarily the guys doesn't care.  What it comes down to is  being uncomfortable in front of a camera.    Primarily, they don't know what to expect.  Here are a few items that might make the shoot go smoother for you and your man. 

•  Give him plenty of notice of when the session is. Make him put it on his calendar with reminders. Put it on the refrigerator.   Mental preparedness is key for most guys.  Talk about your photo session in advanced and tell him what your ideas are, and ask him for input. Collaborate on a setting and on dress style. He will enjoy the session if he has a vested interest in it and you will have a better time during the session as well.  Continue to talk about it as the date draws near.  Keep it on the front burner.  Let him know how important it is to you.

•  If possible, a couple of weeks in advance of the session, have the photographer talk to the bride and groom together about how the session will flow and make sure you feel like the photographer knows how to pose you as a couple.  Maybe even the buzzwords the photographer uses to pose you.  I sometimes will just roleplay a single pose at a meetup session.  Something simple.  If the guy feels confident, it will show in the images.

Physically Prepare Him

• Clothes  Actually put on the clothing you both will wear at the session and together look in the mirror.  Make sure the clothes are clean, neat, and somewhat wrinkle free.  Make sure the clothes fit and are not too tight or too baggy.  You might even practice your hugs and kisses...but don't get too wrinkly!  
• Hair:  If he needs a haircut, make sure it get's done about a week before the session so it looks more natural.  Full beards need freshening up, trim, neck cleaned, eyebrows cleaned up...etc.  Many guys are ok with their everyday appearance, but a little preparation will show up in your final images.  It makes a difference between vacation snapshots and engagement photos. 
• Socks and shoes(optional).  Unless you're doing a barefoot shoot, then, yes he'll need matching socks and appropriate and clean shoes.  Cowboy boots are popular in this part of the country, but it all depends on what style you are going for.  If boots are part of the ensemble, make sure they are clean; no fresh samples from the ranch necessary.
• Ties are great for formal style, whereas bowties lend more character(think, Dr. Who)  but not everyone can pull off a bowtie.  If he can't tie the tie, get him a clip-on.  Also a tie clip of sorts is a great accent piece and keeps the tie in place.  Make sure the tie color/material/texture complements his shirt.  No tie with short sleeve shirts.  Suspenders or belts; not bot
• Hats  Again, cowboy hats are popular around here, but guys tend to hide under them.  The photographer will have to have him tilt it back to see his fresh face whereas the hat doesn't sit right.  It can be done, but not always.  Ball caps are out, unless you are going for a sports theme.