I am about 10% through a project of scanning every colour neg I have made since 1979. I use a branded film cleaning solution (mainly isopropyl alcohol) and pec pads. A wet pad and a dry pad which I replace after every 4 or 5 pages.
Clean with the wet pad and a dab of solution followed by a dry pad wipe down. The before and after is quite noticeable on 30 year old colour negs which have been kept in sleeves in a mostly clean and dry cupboard. It is also evident that colour negs will not last forever and some labs and films are/were much better than others!
I also tend to inherit all the old family B&W negs. For some (e.g. roll-your-own, chain-smoking grandfather) I have soaked and washed in a mild detergent rubbing gently with a pec pad and then rinsed in washaid, dried and finished finally with the process above. Was successful in removing specs of tobacco and other unidentified dirt from some of the worst affected.