Clematis - a big subject, but if you're really asking about how to give your Clematis armandii a good start, then this should help.
Dig over the area where you want to plant it, enriching the soil with composted manure - when you dig the hole to plant it dig it a bit deeper than the existing rootball, and once you've turned the (well watered) plant out of its pot, plant it so that the bottom inch of stems is also buried below the soil. Water in well. It will benefit from a mulch of composted manure each spring, onto damp soil, but unless you're in a cold region, this variety usually romps away to the point where you're starting to wonder whether you should buy a machete as time goes by. With regard to pruning, this should only be carried out if necessary, and always immediately after flowering has finished - this variety flowers in spring on wood grown the previous year, so if you cut it back in autumn, you lose your spring flowers. (Note: all this is also true of your Montana variety).
This method of planting is useful for all clematis, in particular, the hybrids - with these, it's best to plant the root ball at an angle, so its half laying on its side, with a good 3 inches of stem buried below the soil. Clematis is divided into sub groups - first there are the Species, of which C. armandii is one, as is the Montana you mention, then the Hybrid clematis, usually large flowered, and this group may suffer from Clematis Wilt, unlike the species. They are then further sub divided into pruning groups, listed as Prune group 1, 2 or 3, and these groups are related to when the clematis flowers. These pruning rules can be simplified to just this - none need pruning at all, except for the Jackmanii hybrids, which are Prune Group 3, meaning those that flower from around July onwards, up to autumn. These flower on wood grown in the same year, so usually put on a lot of growth in a season, therefore its sensible to cut them down to 2 buds from the base, or about 8/10 inches from the ground, between midwinter up to just before spring, otherwise, there will be a long section with brown, bare stems and all the growth will be at the top the following year. Which may not matter at all if its climbing up into a tree, when you may actually want the flowers really high up.
All clematis like a deep, cool root run and fertile soil; in hot sunny places, its wise to either mulch or cover the roots in some way to help keep them cool, and to provide plenty of water during dry spells, particularly in their first two years. Water deeply when you do it, and avoid frequent, short watering.