I have handled several guns with varying degrees of dirt. I use a soft rag,warm water, and gentle dish washing detergent ie;Dove etc. On light surface rust I use reconstituted lemon juice and oil free 4-0 steel wool.I once had an 1863 Springfield CW musket with a frozen rear sight.It took a couple of weeks until I had it functioning perfectly.I am a reenactor and in the South a gun can get surface rust quite easily overnight in a tent even in a case. I carry lemon juice and 4-0 steel wool and it does the trick next morning. One thing here is that lemon juice doesn't seem to affect patina As to antique guns when I have cleaned the dirt off I just simply hand rub the wood . It takes tine but I just sit in front of the TV, apply hand and nose grease and hand rub. Admittedly this process is time consuming but being retired I have the time. When ,and this is highly subjective,I am satisfied and IF I want to use something on top of thr wood I am a believer in Kiwi shoe polish, black,brown,and neutral or they can be melted and blended.Incidentally I'm still hand rubbing a French fusil Ca,1700-1730 which I got about three years agosss and the results have been great.What I'm doing is really only replicating one or more centuries of handling.
As to the brass I do the same handling but have on occasion used black powder residue either by putting some powder in a bowl igniting, adding some drops of water, and wiping on or using a dirty cleaning tow or patch.
Other's mileage may vary
Tom Patton