Prime, Paint, Gloss Coat, Paint, Dull Coat - confused

The very first thing to do is to CLEAN the model. Use 91% alchohol or a commercial cleaner like Plasti Prep".

Hand oils cause no limit of mischief.

As you get more involved in plastic modeling, you will start filling seams, removing scratches and otherwise making improvements to imperfections. Those really cannot be "hidden"with coats of paint. In fact a well-applied job of thin layers of paint will bring the flaws out.

Assemble, putty and fill gaps, sand, prime those areas to see what you need to keep working on. Do it all again. When you are happy with what you have, rub it down well and clean it.

Then start the overall priming process. As far as color, it has more to do with thickness and fine consistency. White or gray are most common; black is fine if the finish will be other than white and even then it can be made to work.

Don't try to get too fancy with shading until you are entirely comfortable applying solid colors with thin coats, good coverage and no glitches. 

Bill

I would say the first two guys got it right.  Only thing I will add is be patient.  I've been modeling only for about a year and a half and this still confuses me sometimes.  The order of things can be daunting.  I watch modeling videos and read anything I can to get a process that works for me.  I clean the assembled main frame, prime, paint, clear coat(most of the time rattle can), decals, seal (gloss or flat depending on the subject), oil paints or powders for weathering, and final clear coat.

Yes always prime. Good to show errors and to give the paint something to adhere to, The gloss is to give the decal a uniform serface to lay on so no air bubbles cause silvering. It Protects the paint from issues with the weathering also. You have the right idea. Others will help too.

Th order you have there is generally what I do.  Gloss coat as decals need a smooth finish to adhere to otherwise you get slivering. Also the glosscoat will protect your finish while weathering/washing.  Just do your research/testing regarding paint type interactions.  Last coat seals everything up and gloss/flat depends on what you are building.  All general advice.  There are exceptions such a Natural Metal finishes depending on your choice of paint/material. 

Dark preshading sounds like what you are referring to which makes sense. But for the color coats I always go light to dark.  Again, there are exceptions.