As said before www.detailingworld.co.uk is a good place to visit.
As well as using a lambs wool mitt or microfiber mitt and the two bucket washing method there are some other basic rules.
Like hose/jet washing the car down to loosen dirt before washing. Choice of car shampoo, WARNING ensure you use a good shampoo, as some shampoos will strip off the wax leaving your car unprotected.
If you think the choice at your local Halfords is vast then it gets even bigger on the net. There are tons of products you can buy and it depends on your paint type/colour and budget amongst other things.
As said before AutoGlym products are easy to get hold of, some people slag AG but if used correctly they can achieve a good finish.
Assuming the car has swirls and scratches then AG’s super resin polish, when used with a foam applicator and just two to three bean sized drops of the product, worked into the panel in straight lines(front to rear) works well. It has slight correction and fillers that mask swirls so it is pretty safe to use.
The protection it leaves behind is not great so you need to put a wax on top. AG’s HD wax is very good, as is Victoria Wax - Concours Wax.
Halfords also do a good range of Meguiars products(including kits with shampoo, wax and applicators etc) which are also pretty good. I use their gold class shampoo on my black GS430, my brother uses the gold class wax on his black fiesta and it looks good.
Meg’s also do NXT Generation Tech Wax 2.0 Car Wax, which is meant to make black paint more black, heres a vid
.Hope that helps.