One problem I've found with painting plastic figures is priming them. I've always used Humbrol enamel paint for this in the past and have had no problems using it on metal figures. However, this has not worked as well on plastic figures and so I've been looking at other brush on primers to use and have found an excellent product - Vallejo Acylic Polyurethane Primer.
As can be seen the product comes in multiple colours and bottle sizes. I have only used the black primer so far and I am very pleased with the results. The paint is applied as it comes with no thinning required as it contains a self-levelling medium that ensures the miniature is coated without hiding small details. The primer has worked well on the plastic figures and the resin bases that I use (more on these in a later post) although I've yet to try it on metal figures, when I do I'll post the results here. The primer can also be used through an airbrush without thinning.
If you normally sand your figures after priming then this product may not work for you as once sanded through the primer tends to lift. I'm guessing that this is only an issue for large scale figure painters as it's not something I've ever had to do with 28mm (and smaller) scale figures.
The second unit of Tomb Kings skeletons are nearing completion and I should have photos up shortly.