my son's 19-months old too and has started to feed himself. I always give him a spoon of his own and I have one. He basically copies me and I think finds it a new challenge to feed himself. It helps if you are eating at the same time so they can copy you exactly.....sometimes he feeds me...which is fine too!
often, if I load his spoon and leave it on the side of his plate and he will pick it up, he also loads it himself sometimes. I find porridge good as it's sticky.
At the moment I feed him more than he feeds himself, but i think it will switch and he'll feed himself more than I feed him as time goes on.
I don't rush him. I praise him when he does feed himself. I absolutely do not worry about mess.
Apparently, telling them off about mess, or generally being paranoid about it and cleaning up as soon as they drop it is the fastest way to them becoming fussy eaters later on (and I can well believe it....my sister's son, now 8, is excruciatingly fussy.....and my sister is excruciatingly mess-paranoid!). My son rarely throws it deliberately, and if it ends on the floor is usually because he's dropped it by mistake (he has even started pointing at it on the floor and saying 'uh-oh').
The more you get irritated by mess, the more they will see they can get a reaction from you that way....and you know how much they love doing that!