One of the biggest worries for any modeller is making a mistake with an expensive model. This can be due to a new paint scheme, a new technique or using some new product.
You can reduce this risk by visiting your local store and picking up a cheap model kit you can practice on. If you are painting a historic vehicle then you can probably find a small scale model of the same item. For instance I used a 1:72 scale Sherman tank to practise before I painted my 28mm Sherman tank. But a quick search in your local hobby store will turn up model figures, aircraft and even dinosaurs you can practise your techniques on relatively inexpensively.