If you develop a one coin routine make it a multiple effect, not only a "it vanishes in this hand, and it reappears in the other" (without discarding this effect)
Remember that a single coin can travel to many other places than just the hands (lapel, performer's pocket, spectator's pocket or sleeve (Sanada gimmick), or shoulder, get hooked in the air (John Ramsay), to the table under several objects like coffe cup, a salt shaker (Al Goshman), crossed cards (Al Schneider) or into a bread roll, a sugar packet, a tic-tac box, a lighter)
that it can be bent, erased (David Roth), dammaged and get restored
that it can change in nature splitting it from its glass core and a liquid drop of metal, or change from copper to silver and then to gold (three way Spellbound, Sol Stone tumble change, Derek Dingle feint, Fred Kaps feint)
that it can be pierced by a rolled bill, a pencil (Michael Ammar, David Williiamson), or a finger (karate coin : I like Eric Jones handling among others)
that it can go through a handkerchief (Al Schneider) even a transarent one
... and into a bottle (if you are smart enough to keep this for a finale and not take the coin out of the bottle (leaving with the coin in the bottle to confirm the impossibility that a retrieval destroys)

All in all get prepared for a seemingly impromptu series of effects rather than just showing off in sequence the various sleights you may know ... for just one repeated effect.

PS : don't ask spectator to "mark" the coin, ask him to draw glasses or moustache or hair (or color the wings if it's an eagle)... and then tell them to initial their art work on the tail side just in case they would become famous designers

Head and shoulder the shampoo coin https://youtu.be/KnTvx4Jpd6Y

a one coin reotine

If by routine, you mean vanish, then yes.

It is a routine with one coin. A one coin routine doesn't have to have 20 phases.

It has to have more than one phase, I would argue. "A sequence of actions".

When done for the real world there is alto of interaction saying the coin is on the shoulder person looks after you take coin and it reappears on the table
thiks is just a little quickie no need for more than one phase

Well, it's a vanish and a reproduction.

Yes, and that is a routine. A short routine, but a routine none the less. Of course terminology doesn't really matter in this case, so lets just drop it.

There is a nice one coin routine on Sick by Ponta de smith
Also Jeff McBride's routine in The Show Doctor is fun to do and watch

My "None of the Above" is a unique and engaging routine with one coin that is available in ebook form from Lybrary:

http://www.lybrary.com/none-of-the-above......102.html

I posted a routine with a single coin and a pen on the Perverse Magic thread of the Genii Forum on November 23, 2003.

I think this is the best advice. Work on established routines until you figure out ways to 'improve' them, then follow your heart. (I hope it's good advice; it's the approach I take.)

That said, my two cents:

I like Tim Feher's One Coin 2.0:
http://www.vinnymarini.com/download/onecoin2.html
It's a clean, practical one coin routine, intermediate but not daunting.

And I would recommend any of Marion Boykin's routines on that site as well.