It kind of depends on how bad your cladding is...
As a first step, try a good wash and dry...
...then a liberal application of Mothers "Back to Black".
Apply in the shade, I use a sponge....and be pretty generous.
Give it 10-15 mins to "soak"...
....then wipe over with a clean cloth to even out any streaks.
This has always work well for my cladding.
Jo