White seems the logical choice to highlight red with but unless you are very careful with it's use 9 times out of 10 all you end up with is varying shades of pink. Yellow can be useful but again you need to limit it's use to more extreme highlights or things will end up too orange. :angry:
Red can be an awful colour to get decent coverage on for starters but I have found that by using GW's Mechrite Red Foundation paints you get one coat base coverage. Don't worry if it doesn't look the right red when you use it as a basecoat because it is easily hidden by your red of choice when applied over it. 2 coats for a great red base and no detail fill in.
Now, getting down to the actual painting..... The most useful tip given to me by one of the best fantasy figure painters around is if you want to avoid the traps of highlighting red then don't highlight it.
That means start with the lightest red you wish to use rather than a midtone and only apply shading making it gradually darker where necessary.
As a result, painting red is now one of my favourites rather than one I avoid.
If you still wish to highlight when finished then you can apply either a salmon (preferably) or an orange/yellow to the most extreme areas.
For another piece of useless trivia, when painting red I use the following Vallejo Model Colour paints....
817 Scarlet - 909 Vermillion - 908 Carmine Red - 926 Red - 814 Burnt Cadmium and if you want to go really dark you can either apply a touch of black to the Burnt Cadmium or use 859 Black Red.
For small areas just cut out a colour or two
Some of the figure painting sites are great for advice on painting certain colours.