From the wiki page on Old Believers
Old Believers use two fingers while making the Sign of the Cross (two fingers straightened, three folded) while new-style Orthodoxy uses three fingers for the sign of cross (three fingers (including thumb) held together at point, two fingers folded). Old Ritualists generally say the Jesus Prayer with the Sign of the Cross, while New Ritualists use the Sign of the Cross as a Trinitarian symbol. This makes for a significant difference between the two branches of Russian Orthodoxy, and one of the most noticeable (see the picture of Boyarynya Feodosia Morozova above).
Old Believers reject any changes and emendations of liturgical texts and rituals introduced by the reforms of Patriarch Nikon. Thus they continue to use the previous Church Slavonic translation of the Greek texts, including the Psalter, striving to preserve intact the "pre-Nikonian" practices of the Russian Church.
Old Believers only recognize performing baptism through three full immersions, in agreement with the Greek practice, but reject the validity of any baptismal rite performed otherwise (for example through pouring or sprinkling, as the Russian Orthodox Church has occasionally accepted since the eighteenth century).
Old Believers perform the Liturgy with 7 prosphora, instead of 5 as in new-rite Russian Orthodoxy or a single large prosphora, as sometimes done by the Greeks and Arabs.
Old Believers chant the alleluia verse after the psalmody two times rather than the three used in the Nikonian reforms.
Old Believers do not use polyphonic singing as the new-style Russian practice, but only monodic, unison singing. They also have their own musical notation: not with linear notation, but with special signs — kriuki or znamena ("hooks" or "banners"; see Znamenny Chant). Old Believers practise several different types of Znamenny Chant: Stolpov Chant, Great Znamenny Chant, Lesser Znamenny Chant, Putevoi Chant, Pomorsky Chant(or Khomov Chant), Demestvenny Chant, etc. In this respect it represents a tradition that parallels the use of Byzantine chant and neumatic notation.
There's also a chart on that page
that shows the main Nikonian reforms vis-a-vis the Old Believer practice.