This is a far from exhaustive list but covers some key areas. You can jump to a specific topic by clicking on the links below:
Scratches in Glass
Almost all glass used in boats is toughened (heat tempered) glass and by the process of annealing, the surface is very VERY hard indeed. If you have a large or deep scratch, there is virtually nothing you can do about it other than replacing the glass (which we can do).
If the glass has a small scratch or a metal abrasion mark, this could be removed (polished out) with the use of an electric drill equipped with a polishing head and a Cerium Oxide solution. There are kits available (but not from us) and should contain all the necessary parts and instructions for you to carry out the job.
Scratches in Plastic
As with glass, if the Plastic has a deep scratch in it, this cannot be removed. If your Perspex is crazed, this too cannot be effectively polished out; the crazing is caused by the effect of UV light on the material and can be up to 3mm deep. If Polycarbonate, it's likely the panel will have a yellow tint and this too cannot be removed.
To remove small scratches, obtain a couple of pieces of soft cotton cloth and a bottle of liquid car polish that does not obtain any abrasives. Do not use a colour restorer (T Cut) or pre-coloured car polish or the hard wax polish in tins. On a small area first, apply a spot of polish on the cloth and rub in lightly. Leave to dry and remove the residue with the other cloth. Repeat if necessary.
Using car polish once or twice a year on your Perspex keeps its appearance and can offer some protection against minor abrasions.
Another obvious comment is to be careful what you use when cleaning windows. If it is in any way abrasive it will scratch as well as clean and whilst dirt will reappear, the scratches won't go away....
Exposed plastic
Exterior plastic (think hatch handles and friction lever pads) suffer when exposed to salt and UV. Grey goes white, Red goes white, Black goes grey etc.
Most of the time the parts are structurally fine, they just look weathered.
There are a number of liquids which promise to return these to their original colour and they all will for a limited period. A liberal covering of margarine does this too and lasts about as long. Don't waste you money.
The solution we use is to paint them. We clean with wire wool (stainless steel please) and/or a scotchbrite pad along with white spirit. We then dry and wipe over with acetone (to remove the oily residue from the white spirit). Then a coat or two of spray primer and then repeat with top coat. We use PlastiKote spray paint available from Amazon. The tins shown are Primer Grey, Matt Grey and Satin Red (for the release pins in Lewmar hatch handles). We also use Matt Black (for the tops of Superhatch handles). So far no complaints...
Moving parts
Hatch handles and moving parts on opening windows should be cleaned and lubricated at least once a year. We can often source new exterior handles and pads (eg Lewmar Ocean friction lever pads). O-rings are often standard sizes so consider getting some and replacing as required.
Channels in sliding windows should be cleaned out every year and if the sliding action becomes difficult, apply some silicone gel or maintenance lubricant (but bear in mind this may not have a lasting effect). Also, make sure any drain holes are clear as if not the water will likely end up inside your boat. Sliders - the devils work - a window which can never truly be watertight!