As practically everyone says above you need to:

1. Clean off the rubbish and staining. 
2. Polish (technically polishing is removing part of the surface) with minimum abrasion - (T-cut and Cif are considerably coarser than most people need)
3. Protect - using wax or glaze. This adds a new coating that can itself be buffed to a shine.

We (BoatSheen.com) do a pre-wax treatment that combines cleaner with polish, so you can do the first two steps in one. It's not the same as car polish. Fibreglass is much softer than most car paint, and the chalking from oxidation grips the surface - on car paint it washes away much more easily.

Choice of wax or glaze depends on how long you want it to last. Waxes remain as wax coatings on the surface and can be removed relatively easily. Of the various waxes, carnauba wax is hardest and gives the best shine.

Glaze systems are curing products that bond to the surface, so properly applied they last longer than waxes.

Machines on fibreglass

With machines on fibreglass you need to make sure you don't overheat the surface. Again this is different from car paint finishng, where friction heating contributes to the process. 

Sander-polishers need to have a low setting - around 600 - 1000rpm maximum and need a bit of skill and concentration to avoid damage. Orbital polishers are easier and faster for just polishing and they won't overheat the surface. There's a polishing machine comparison on our web site.

Hi Jerry. We watered it down. Sorry, can't remember the concentration. Wallpaper paste actually sounds like a good idea, so long as you don't leave it on too long!

Hi John. I'm not supposed to allow blatantly commercial posts, but as you have included some useful general info I'll let you get away with it this time!

Hi Cathy

Thanks - I'll keep it technical rather than commercial in future!

John 

Well first stage in process appears to be-leave boat on mooring on west coast of Scotland thru some of worst gales and almost continuous rain-result much of the mold collected whilst mooring near trees has been stripped off.Got to my boat for first time since Christmas-too long really.But apart from shredding my outboard cover and finally finishin off my mast to boom cover and poss. an anchor tripping and resetting(one of three  Bruce types Anchors)I have never seen the boat look so clean!Even the non slip deck tread does not look green!and the hull just really needs a quick wash and polish.Not that I like the idea that an anchor has tripped but the we had our force 11/Hurricane 12  back in Feb.

Phil

After thorough cleaning with acid or any decent proprietary cleaner, I have always used 'Mer' car polish, and providing it is applied in reasonably warm conditions I find the results to be excellent. I use a fairly slow revolving electric buffing machine fitted with a lambswool bonnet and the hull gleams. The beneficial effect lasts for most of the season.