Ingredients - rice
Risotto rice - any are fine, so I tend to use Arborio due to it's easy availability. I guess around ~ 100g for eight arancini
A little veggie stock adds some nice flavour
Ingredients - filling
The traditional filling would include chopped tomato, a little finely torn prosciutto, finely cubed mozzarella, basil and peas. However this really is a free for all - I've even done some with veggie curry in for Indian colleagues and it worked well. Mushroom and tarragon works brilliantly, likewise smoked salmon and dill. Ragu is also very popular & works very well. Whatever you choose, you'll be looking for little more than the volume of an individual yoghurt pot for ~ 8 arancini, and whatever the filling roughly mix the ingredients together
Ingredients - coating
1 egg to about 8 arancini
breadcrumbs - around 2 slices of bread for 8 arancini. If you want to be super-fancy, then try with sesame seeds instead, but this requires more of a no-hands technique. Dried or stale breadcrumbs work fine, indeed they are a little easier.
Ingredients - Cooking fat. Vegetable oil or similar is ideal, but not olive oil. It can be re-used once cool, but I only tend to get 2-3 uses out of it before binning it. I use a large quite deep saucepan, but this would be easier in a chip fryer. Either way, do take care as no-one wants a fire with that amount of hot cooking fat around.
cooking the rice
Cook as per risotto (using the veggie stock and even a bit of grated parmesan to add a little extra flavour), but you want to over-cook it a little, so that the rice is starting to break up / becoming very sticky. I also try not to overfill with water, so that much of the water is removed by cooking, and what's left gets absorbed as it cools. Now let this cool, otherwise you'll get burnt hands doing the fun bit
Making your balls

take a little of the now cool and stodgy rice, and flatten in on your left hand so it's covering the fingers and an inch or so of the palm. The overcooked rice is key to this as it squishes nicely into place.
With your right hand grab a little of the filling, maybe a teaspoon or two max and place it in the middle of the rice on your left hand. Now close your left hand forming a ball around the filling (it usually requires a little extra rice dabbed into any gaps). Give it a good but gentle press all around the ball to make a good seal. Put that one aside and do the next one and the one after that. Every 3-4 balls you'll probably need to rinse your hands as they get very sticky.
Once all balls are made, get the egg and a small bowl, plus the breadcrumbs and a larger bowl or dinner plate
Beat the egg and roll a ball in the egg to coat the surface, then roll that in the breadcrumbs to get a complete coating. Then do the same with all the balls.
To the fryer! Heat the oil up until a breadcrumb dropped in clearly sizzles. Use a slatted spoon to lower the balls into the hot oil, putting only as many in as fit (they need to be mostly submerged). Cooking time isn't important, but aim for a pleasing golden colour. Usually only 4-5 mins IIRC (I never time it). Give them a gentle roll in the hot oil to ensure they are cooked reasonably evenly.
Once you're happy with that golden colour, turn the heat down/off to lift them out, placing them on some kitchen roll to absorb some of the fat. Now turn the heat back up and repeat for the remaining balls.
In theory that's it, they can be eaten straight away, however I slightly prefer them left to cool and then reheated in the oven (the usual 180C does fine for about 8-10 mins).
Serve it simple, either as it's intended mid-morning 'filler', or if served up at the dinner table, with a leafy green salad.
Loads of variants possible - e.g. a little spice in the breadcrumbs, whatever filling appeals, indeed you can play around with the stock (e.g. I've used Saffron before and that comes through nicely. The trick with this dish, is the ability for rice to provide the bulk, but also the canvas for other flavours.
Happy to answer questions - I've got a written recipe somewhere, but haven't used it for 2-3 years. The technique is very natural, so easy to learn.
regards
Ian
p.s. FWIW Arancini is the plural, a single one is an Arancino. IIRC the name translates as little orange(s).