Specific primers?

Different primers for different purposes, the basic idea is to present an even surface for further painting.

If you are painting a kit with photo-etch, resin, or kit bashed from differing colour plastics, then priming is a good idea, as is washing it with liquid soap, lighter fluid, or similar.

If you are painting Metallics, NMF, metal foil, etc, then priming is a must.

Some people ALWAYS prime, some NEVER, some in-between, but it depends on a lot of factors, & preference.

eg., I usually do, as I prefer Vallejo ModelAir, which doesn't always stick well to some plastics.

Primers:

Rattle-cans: Canned automotive ACRYLIC paint with a lacquer/Cellulose smell, stick like the proverbial to a blanket, & can be further sanded, etc.  

Go to a reliable car parts dealer/home depot rather than a 3/€/$ store!

In the UK, Halfords' Grey or white are popular with air & armour modellers.

MR Surfacer, in 600, 1000 & 1200 fine-ness is sold as a sprayable, if very stinky primer, but the 600 grade can be used to add texture to cast armour for example.

My Favourite at the moment: is Vallejo Polyeurethane Primer, sticks well, available in many armour colours, OD, Russian Green, UK Bronze Green, Rot-Braun, Dunkel-Gelb.  needs to be sprayed.

Minitaire, (a new to the UK range, distributed by Humbol), have a similar primer, but I haven't used it yet.

Many figure painters swear by Humbrol for base-coating, under acrylics or oils.

& 1 armour guy I know primes everything with Vallejo ModelAir black.

I would advise NOT to practice on that £/€/$ 100.00+ kit, get a flea-bay, junk-yard sale kit, or that old one from the back of the stash to practice on,  then you can have more fun, practice, try new techniques, without worrying about trashing an expensive, rare, or cherished kit.

Good luck

My 2 favorite primers are rattlecans

Mr Surfacer 1200

Tamiya Fine

It's not 100% necessary to prime,but I have gotten in the habit,especially when using resin and metal AM accessories.I also prime all of my figures.

Jon_a_its

If you are painting Metallics, NMF, metal foil, etc, then priming is a must.

I'd have to respectfully disagree here.  I have finished about nine 1/48 aircraft in one type of NMF or another and did not prime any of them.  Immodestly, I have to say that they all turned out fairly nice.  In fact, guided by what I had read in FSM, I was advised to apply NMF-type paint onto bare plastic.   I just don't think "it's a must".  Your mileage may vary.

Gary

Here are a few examples:

I've used Tamiya Fine primer from the spray can which is very nice.

However, nowadays, i prime with paint rather than a dedicated primer.  The colour i prim with will also be determined by the overall paint job i'm applying - eg, do i want shadows (so prime with a dark colour), will the top coat be a light colour (so prime with a light grey or white) etc.

Thank you very much for the tips/advice above!

My favorite primer is Krylon, in spray cans.  They make a gray, a red (red oxide color) and a white.  I find the white is not a gray primer, hard to cover.  If I am finishing with white or yellow, I apply coat of gray primer then the white.  The red oxide covers and primes well,  I use it on ships that will have a red oxide bottom.  So the primer becomes the bottom color- I mask off the bottom and put the gray, white, or whatever hull top color over the red oxide primer.

After seeing an earlier post from Don about using Krylon spray primer in a rattle can, I decided to try it myself on my most recent WIP.  I used a grey primer on my F-16D and it worked great!!  Even though the grey was almost the same color as the dark grey that I was going to use on the finished model it covered very well with the lighter grey.

A couple of super fine coats of primer and the detail really popped!

Thanks to Don for the information!

Seemed to thick to me.