It's pretty funny how they are worried about the glass being right against the paper possibly creating a problem in the future but they have no qualms about sticking it down with ATG!!
Either the piece is handled using the best practices or it isn't. If you are going to just stick it down with ATG tape then you aren't worried about long term care of the piece and the glass against it won't be a worry either.
If you are asking for the best way to do it then...
The proper way is to hinge it from behind using a wheat or rice paste and mulberry paper hinges.
A slit is cut thru the acid free board it is to be mounted onto and after the strips of mulberry paper have been glued to the back of the art... that strip is fed thru the slit and then attached onto the back of the acid free board. This the most noninvasive/reversable way to mount art. Any of the other adhesives will transfer solvents to the art and eventually leave a stain. Remember how old scotch tape leaves a yellow stain after it has been on paper a while? That is the solvents in the adhesive and thus the damage to the art.
Now, if you just want to display it and aren't worried about the long term, then you might as well ATG it down and be done with it. I always like to see the edges of these pieces as that is part of the charm of it. I like to give it a floating look by mounting it to a smaller piece of board so it raises it up off the colored background. This accentuates the edges of the paper. When it is ready for the frame, a spacer is placed between the glass and the colored background mat board which keeps the glass off the art. The main thing to remember is to make sure the frame you choose is deep enough to actually hold all of this. Nothing worse than picking out a frame only to find the package won't fit into the depth of the rabbet.
For Julies post...
You have the right idea and my hinging method will work there, also. One of the problems you have is the uneven surface of the art. Is it a watercolor or what? If it is a watercolor and you want it to lay flatter, you can actually flatten the paper by lightly dampening the back of the paper and put it between blotter paper and weight it down till it dries. It will be flat. Again, I like the unevenness of these things and like to accentuate those features. After you have mounted the piece, you should build up a spacer of foam core behind the mat so it brings it up above the face of the paper. It creates a "well" effect as well as keeping the glass off the art.
To blow my own horn ever so slightly, I have a frame shop for the last 13 years and have a Certified Picture Framer title so that is where my suggestions come from.