So my car was looking a little sorry for itself as the plastic trim around the wing mirrors and the rest of the car were looking grey, especially the mirrors. Thanks to someone on here (can't remember who, sorry) I heard about Autobrite's "Berry Blast Endurance Trim & Tyre Gel". (This can be purchased here). This stuff works by leaving a very fine, clear film over the area applied.
I bought some and thought I'd give it a go, below is the method I carried out - Photos are below my rough guide!
1) First thing to do is make sure the trim is clean and free of bugs etc, this product really does work better if the area it's going on is very clean - ideally give the whole car a rinse before hand!
2) Apply a small drop of the Berry Gel (smells amazing by the way) to a foam applicator pad such as as this.
3) Apply the gel to the required areas but don't put too much on - you'll be amazed at how much area you can cover with a small drop.
4) Leave to dry and be happy with the results.
5) Optional - apply to wall of tyre as a tyre dressing, you should only need about 4 drops max of the gel.
And here's a couple of photos after I'd done the rest of the car and left it about an hour in the sun to fully dry.