For a posable (multi-part) prop:

The mesh parts should stand in the correct position relative to each other, and be at the correct scale when imported into Poser. Things that have a front side (a car, a gun) should face an un-rotated main camera when imported. Each mesh group (part that needs to move) should have a unique name that is both short and descriptive. Eg "rFrontWheel", "lBackDoorHandle", "rBackSeatBottom", "rFrontSeatBack", "rFrontSeatBottom", "petrolCap". A wheel does not need a separate Tyre and HubCap group (unless you want to change a flat), but should probably have separate material zones for the Tyre and HubCap.

It also helps if the names of the material zones are short and descriptive. Don't have more material zones than you need. Eg, with a car, there is no need to have a separate material for each seat, they could all share the same "SeatCloth", material, though you might want to have a separate "SeatBack" material.

Follow the steps for a single part prop, for each part, up to and including step #3.

Parent the props together to form a hierarchy of rotational precedence. Eg the chassis is the parent of the wheels and doors, the doors are the parent of the door handles.

Check that everything rotates as desired, and make any necessary adjustments to origins, orientation, or rotation order of the various parts. For example the steering-wheel of a car should usually rotate round the z axis (with a truck it might be y), but the z axis needs to be tilted to match the angle of the steering column. Perhaps rather counter-intuitively, in the Joint Editor window, you use the 'xrot' dial to set to orientation of zRotate for the steering column.

In some things the rotation order can be important. Poser joints work like a series of three gimbals (think of a ship's compass, or a gyroscope). Each rotation channel is equivalent to a gimbal. I'll say some more about rotation order in another post. Now to continue making the posable prop.

Memorize everything (Alt+Ctrl+A).

Adjust the material settings as desired.

Select the prop at the base of the parenting chain, eg for an auto-mobile the chassis. Click the "+" in the Props palette. Use the "Select Subset" button to include all parts of the item, and save it to the palette.

If the item is to be a smart prop, open the pp2 in a text editor and find any lines that say "parent UNIVERSE", replace them with "smartparent NameOfParent".

With a posable prop some transforms are often not desirable, eg rot a steering-wheel, you may want it to zRotate but not translate or have any other rotations. In that case you need to make some edits in a cr2 editor (or a text editor), for all translate and rotate channels in the steering-wheel, except zRotate, you need to force the limits, and set the min and max limit to zero, eg:

            forceLimits 1
            min 0
            max 0

You might as well hid the dials for the locked channels, so now you have:

            hidden 0
            forceLimits 1
            min 0
            max 0

I have tried to go into a lot of detail of things you might need to know (perhaps too much) . But start simple, and experiment, eg a box prop with 4 rotating wheels made out of Poser cylinders, then work your way up to more complex things. Experimentation is the key to learning, you can read as many posts and tutorials as you like, but you will never really master these things unless you experiment!