I have to make this small entry, to save someone out there from the butchering I saw was once done to mugo pines.
Now is the time to snip the new growth, called candles, which is how these pines should be pruned. I usually just cut them half off with shears. Occasionally, in the type ( mugos vary) that grows larger I will cut out the odd branch or two to shape it, but don't ever cut pines into their old wood, such as a massive pruning that is done on some deciduous bushes.
Mugho Pines are dwarf trees, and they keep their shape well with yearly attention in the spring. It doesn't take very much time to trim them.
I haven't seen them this year, yet, but my mugos have often gotten an ugly case of caterpillars that strip the needles. I hand pick those and burn them. I suppose you could drown them in something, but I live in the country where we can still burn things. A little bar-be-cue stove would work in the city.
The things we do for our garden!
If you'd like information on how to plant and grow a Mugo pine: