I do it either easy or hard.
Easy) Introducing a miniature to a cob: Cob in the field, mini in the paddock. Only able to see/touch over a gate. Did this for a good week. Put mini in the field after this, and had cob on a line. Waited until both were calm and grazing before taking the line off (at which point they did the "omg new horse" run about. but both were ok with eachother so just grazed after) Any mini i added later was the same, but skipping the 7days in the paddock. Put cob ona line to make sure i could control him.
2) Hard: Let my two minis meet another mini over the fence, next day just let them out together lol (when i had big horses i took them both for a hack together, then just let them out. after untacking)
One time i had a colt in for a training session. He was NOT getting it and after an hour he still was being very difficult. I brought my own gelding in, work them both at the same time and my gelding, knowing the routine, was able to teach the colt in mins. Both had never met, but had zero issues because they had their minds on something else. They have met/penned at shows again no problem.
I try not to faff about too much. Let them sort it out.