The first question you should ask yourself is ‘do I really need to clean the optics’? The reason for asking yourself this question is simple. Too many people clean telescope optics far too regularly. A small amount of contaminant on the lens or mirror will make no difference to the quality of the image, in fact you would be surprised how much rubbish can be found on the optics before any image degradation is seen.
If you decide its the right time to clean then make sure you mark the orientation of the mirror or lens in its holder before you remove it. This will allow you to put it back in the same arrangement. This is of more importance with a lens than with a mirror.
Once you have removed lens or mirror then great caution must be employed in cleaning. The first step is to get rid of all the contaminants which is easily achieved by submersing the optics in a bowl of distilled water (if you are cleaning a lens, ensure its supported and not resting on the base of the bowl). Using cotton wool balls, very gently wipe around the optics using the smallest amount of pressure. Keep a swirling motion going in the water which will prevent the rubbish from settling back on the optics again. Its essential not to apply any real pressure at all as you could easily scratch the glass. You are almost letting the weight of the cotton wall ball provide the pressure. Now remove the optics from the bowl slipping it out so that it comes out edge first. This will keep contamination from getting back to the glass.
Let the mirror dry now by standing on its side. You shouldn’t get any drying marks as the water is distilled but the final task will ensure the mirror is given a final clean. First make sure there are no pieces of stubborn muck or grit that you can see still sitting on the surface. If there is, tease them off with a cotton bud. Once its free from any contamination, take some Isopropyl alcohol and pour a small amount in the centre. Using a very soft towel, buff the surface until all the alcohol has evaporated. Make sure you buff using a circular motion.
And that’s it, you should now have an ultra clean set of optics. One final word of caution with regards to lenses. Most good quality telescopes using lenses are actually made up of any number of lens components from 3 and up. Check the lenses to see if they are very well sealed together. If they are not or if you are in any doubt then take the lens to a professional organisation to get cleaned. You are at risk of damaging the optics if water seeps in between the lens components. If in doubt, seek advice from professionals.