Sizes from 1/16 to 4/4, Rosin, and Tuning G-D-A-E
Before the first note, the violin has to fit the person holding it. Sizes run from 1/16 for the shortest arms through 1/10, 1/8, 1/4, 1/2 and 3/4 up to 4/4, the full size that almost every teenager and adult plays. The measurement is the left arm stretched straight out, from the neck to the middle of the palm. An instrument that is too big pulls the elbow out and leaves the fingers straining for their notes; one that is too small crowds them together. Trying two sizes side by side in a music shop usually settles the question quickly.
Rosin is tree resin pressed into a small cake. Fresh bow hair is too slippery to grip a string, so a bow without rosin barely makes a sound. Rub a thin, even layer along the hair from frog to tip, and add a little more whenever the tone starts to feel thin. Too much leaves white dust on the strings and the top of the violin, and the sound turns gritty. Wipe that dust off with a dry cloth after each session to keep the varnish clean.
The strings are tuned from the thickest: G, D, A and then E, each a fifth apart. The fine tuners on the tailpiece handle small adjustments, while the pegs in the pegbox are only turned when a string is far off, slowly and while bowing. A chromatic tuner app on your phone is plenty at this stage. Tuning at the start of every practice session trains the ear to hear a correct reference, which pays off the moment the left hand begins searching for notes.
A violin that fits, a thin coat of rosin and four strings in tune come before any technique practice.