I haven't personally done introductions but I've read a lot about them. I am think to add 1 or 2 gliders some time in the future to my current pair.
In any case, below are links that describe methods of introducing gliders:
thegliderinitiative.webs.com/safe_intro_article.pdf
www.sugarglider.com/gliderpedia/index.asp?Introductions
After you get your new addition, have him/her vet check with fecals in addition. It isn't recommended to try introductions after a period of 30 days or so of quarantine, after which you should have your vet check your new glider again, including the fecals (this is in case that he/she had any parasites, they would have had time to hatch and would appear positive in the fecal test).
After that you can start some of the methods above. Keeping them in the same room, where at the beginning they can't touch each other but can hear and "chat" with each other. Then gradually move the cages closer. Pouch/fleece/toys interchange between the 2 cages. Then taking them to a neutral area for actually presenting each other, always prepare with fleece or gloves to separate them in case they start fighting.
As for how he will act, it depends on his personality. You know him the best, so you may have some indication from how he acts as to how introductions are going. Some gliders are very skittish, and would should reluctance to having a new friend. While some are just so excited about getting a new companion.
Whatever the case is for your gliders, I wish you the best of lucks!