Here are some tips: https://www.bobvila.com/articles/how-to-clean-brass/
Hard to believe but a quick solution is tomato based products like ketchup, tomato sauce, or tomato paste. Wipe off with a damp rag first or run under water. Once it's dry, you buff in and let sit until it's dry. Then clean with hot dish water. I prefer blue Dawn.
If they are brass and look like real brass chances are they have a lacquer on it. The reason I say this is that brass will tarnish fairly quickly and can turn black. What keeps the brass from tarnishing so fast(and keeps it shiny and gold-ish) is the lacquer which keeps the air from tarnishing. Eventually (takes years), that brass shine will tarnish even underneath the lacquer though. The way to deal with that is stripping the lacquer... then shine up with a brass cleaner once that lacquer is off, and then re-lacquer. Sometimes something will look like it is solid brass but is actually brass plated. In that case check to see if a magnet sticks to it. If a magnet sticks then it is brass plated because real brass is not magnetic. In either case, you could try shining it up with a brass cleaner, if nothing happens to make them look better, you will need to strip it. That means there is lacquer that needs to be stripped to get to the brass. Then try to brass cleaner it again. (TRY BRASSO cleaner) If still nothing looks better, then the metal is probably a cheap metal that has been painted to look like brass and can just be repainted and finished off with another lacquer or polycrilic finisher. Sorry Cleaning brass can be tricky. If it is brass plated, be careful, the plating can start coming off in the process. Good luck!
Rinse with warm water and dry thoroughly. For tougher cleaning jobs, pull out the ketchup, tomato sauce, or tomato paste. Simply rub a thin coat onto the brass, let sit for an hour or so, and then clean the piece with hot, soapy water. Another option is to make a paste of equal parts salt, flour, and white vinegar.
They sell stuff at Lowe's that will work.
There is only one product that I would use on brass, it is called Brasso. Been around for a gillion years. Cleans brass beautifully.
Brasso removed some of the metal. I remember ROTC. For large items ketchup will work. I use a dab of white toothpaste on a damp cloth. For intricate patterns a dab of toothpaste on a damp toothbrush. Make sure it foams up. rinse and wipe.
I sell a lot of items on Ebay. Also works on copper, gold, silver, porcelain, ceramics, sneakers, plastics, etc. For my sales I needed one product for cleaning everything.
Ketchup works wonders