Dirty Copper Coin Cleaning?

Under the circumstances, Pertinax has given the best advice; acetone would be not justified.
Perhaps a soft brush could also help, the bristles of most brushes are considerably softer than bronze.

Abovementioned is usually the first step in cleaning ancient coins after recovery from burial.
Same approach used by metal detectoristists.

Acetone is used mostly for removing glue, oily substances and other stuff that can be dissolved.
Acetone is nice since it evaporates quickly with no residue.
HEED ALL WARNINGS ON THE CONTAINER.

Verdigris is a different story.
Damage has already occurred so VERY light rubbing is not going to make it worse.

Olive oil is often used on copper coins.
It is VERY slightly acidic so will make a coin look better.
It works slowly (weeks if not months).
Just keep an eye on the coin.
Then acetone to remove the oil.

I was told to use a toothpick

Don't use a brush as it drags the dirt across the coin and will most likely scratch it.Acetone
will get a lot of the loose dirt and oil off it but verdigris can be harder to remove .A toothpick
may help but it's a case by case exercise.Photos may help to give advice on your more valuable coins.WD40 will remove heavier dirt and some verdigris but can eat into the patina
if you leave it soaking for too long so you need some experience for best results so practice on bullion value coins first

Thanks everyone. Will post photos when I work out how to fo this.

Be very cautious when using acetone, in my experience it removes the patina.

Also, as I saw recently, it turned a 1949S cent in MS63 RD to MS63BN over the course of a couple of weeks.

Not a disaster for that coin but if you've got scarce mint condition coins with their original salmon-pink colour, it might be.

Thanks everyone.
I'll post pics as doon as I can.