OK, so how do I, "Rescue Vinyl" ?
Perhaps the best way is to use an ultrasonic cleaner. It is a water bath and ultrasonic vibrations are used to cause tiny bubbles between the surface of the record and the dirt. When the bubbles pop, the dirt falls out. However, I don't have two thousand pounds to spend on a machine like that... nor do I have the room for it anyway. So that's out the window.
What I do is a cleaning process that is relatively inexpensive and I use it on second hand records that have seen some action, in order to give them a clean and also digitise them. After all, there is some kind of damage that you just can't reverse. The best that can be done is to clean the record as effectively as possible for the budget, and then keep a digital copy for use in modern devices that can still bring you joy and capture the overall ambiance of the recording. I've bought records from dealers who proudly state that it's been cleaned on such-and-such a machine, and they've still been very clicky and in need of a clean.
Some vinyl had tracks that weren't released on CD but also happen to be recordings of the way that the record was produced in the day. Production is as much a part of the recording as the music itself. Some modern reprocessed tracks just sound awful, despite being technically superior. Such is the nature of the subjective process.
The first thing I'll say, is to not do this with any record or equipment that you value. Get used to the process with an old record, an old needle and then make up your own mind about the process. Also, I'll add in that electronic processing won't save you. You've really got to get the best signal you can off the record, or else you're on a hiding to nothing. Unfortunately, this process can't reverse damage, so if a record is sounding a bit muddy in the trumpets or high frequencies, even with a nice, good needle and being cleaned within an inch of its life, then it's going to be a case of buying another copy. Or else if you know a shop or something, which will ultrasonically clean an individual record for a price... that's a gamble only you can decide to take.
We start by gathering equipment. First up is some 99% isoprop and some horticultural soap. Also, some distilled water. The mixtures are about 4:1 or 5:1, as you wish. You're also going to need a brush. I've got two 12" LC Precision brushes from Keith Andrews; it was an alternative to the more expensive Keith Monks brushes. The brush is sold based on the record size it is meant to clean, not the actual brush size, so be careful. I also had to wait a while for them. These brushes have bristles of a particular strength and concentration that's good for getting in the grooves.
The Isoprop mix is used on overly dirty records, about 4 water to 1 isoprop. The horticultural soap mix is the main cleaning mix, 5 water to 1 soap.
The reason for using horticultural soap is because it doesn't have lanolin, which you will likely find in other detergents like washing up liquid, etc. Water has all sorts of bits and pieces which get left behind when it evaporates, so distilling leaves those impurities behind as part of the process so you get a, "clean," water.
The first thing to do is cut out a cardboard circle and cover the label.
If I think the record is overly dirty, I start by spraying on the isoprop mixture, then get it in the grooves and leave it to dry for ten minutes or so. Use the brush to try and dislodge whatever is in the grooves that you can. Obviously, a lint free cloth to wipe the brush on while you work, is a good idea. The hope is that the isoprop will also dissolve or dislodge some of whatever is in there.
The main cleaning is the soap mix and, like the isoprop, the brush is used to get in the grooves and do what it can to lift and dislodge dirt. I work it in to a gentle lather and take off the excess by wiping the brush in a lint free cloth. That's left for ten to twenty minutes to dry.
If the record is reasonably clean, then I'll only use the soap mixture and I'll skip the Isoprop.
The painful part of the process is getting the soap back out again (with all the crap that it's picked up) and for that, I use a sacrificial needle and give it a few plays on the deck, until I'm getting minimal soap out... and then I record the last play on the computer, using my sound card. This usually requires three or four plays with a minimal (2.6g) needle pressure, which is standard for the Ortofon Red you see here. Note that I've coloured it yellow, so I know it's my old needle. Also note that sometimes, during the final play, I'll lift the needle and clean off the last little bits of soap between tracks, to make sure I'm getting the best signal I can. Recording is done in Audacity, but any software like Goldwave will do you just as well.
Note that I don't use a USB deck. While they are fine for general recording when you don't want a quality signal, they generally don't contain a pre-amp for the needle signal, so you don't get a good digital resolution from them. Amplification is simply done by multiplying the numbers once it's been digitised, usually by a factor of ten in my experience, which isn't good. I mean, it works, but it looses resolution which you can't get back.
Once the signal is off and digitally recorded, I feed the results through a piece of software called Click Repair - http://www.clickrepair.net/ - You should be able to try it before you buy it, to make sure it's right for you. Personally, I've paid for the de-click software. It's open source and made by a one man band, so it's worth supporting. It works by mathematics, rather than by applying a generic filter, so it's better at finding and removing clicks without damaging the music. You've also got control over how aggressive it is.
Finally, the tracks are "topped and tailed" by a one second lead in at the front of each track, which I, "fade in." If you don't do the fade in, then you're immediately hit with track noise when you start the recording, which isn't nice. Also, by running the lead in to complete silence, there's an unpleasant jolt when the music starts, because turntable noise is also present as part of the track. Obviously, the degree that this affects things, depends on the music. I've found a one second fade in, to be the most effective. Then you've got a fade out at the end of the track, and you're done. I usually save as FLAC, which is lossless compression format.
ClickRepair won't get rid of everything and occasionally you'll find a click that it didn't get. Learning to edit the file yourself is important. With practice, you'll recognise the clicks and you'll be able to go in and take them out... just like removing a word from a word processor document. Note that this won't always work and the best you'll be able to do is simply lower the intensity of the click, or in rare cases you'll actually end up creating a click that you can't actually see. It'll be weird when it happens, but it does every now and then. You also won't be able to take out heavy clicks, because that will take out so much of the music that it will cause a small, "jump," because the beat will then be off. It just takes practice and care.
In very rare cases, I've had to cut pieces out of a file and paste them over some damaged areas. It's a bit of a ball ache, but it has been the only way to repair some really damaged work that just can't be masked out. Fortunately, it happened in the chorus of a piece of music, so there was a repeat of the chorus later on in the track. But sometimes you have to admit that a record is just beyond rescue, and so far I think I've bought replacements for about four records so far, in the hundreds I've processed.
Lastly, you can clean out the remaining soap from the vinyl. How you do this, indeed whether you do it, is up to you. I've also bought new sleeves for my second hand records, in some cases keeping special sleeves inside the main sleeve where they've got pictures, lyrics, etc.