The act of Russian can go by many other names: titty-fucking, tit job, tit wank or tit fuck. It involves a man placing his penis between a woman's boobs and thrusting between them while they are squeezed together, to simulate penetrative sex. Sometimes the partner will use their mouth too, allowing the man to thrust between the breasts and enjoy a lick before they slide back again.
For Russian it is best to ensure that there is lube so that the penis can slide easily back and forth. Test out different amounts and types to see which works best for you both. Squeezing the tits together makes a closer, tighter feel around the cock and so can be very pleasurable, if they are not treated roughly. The man or the woman can squeeze the boobs together, though the man may enjoy it as he can play with the boobs and tease the nipples as he thrusts. If the woman also wishes to use her mouth to pleasure him, she will prop her head up at an angle with a pillow to allow the penis to slip easily between the breasts and into her awaiting mouth.
While many say that this is best done with a busty woman, it can also be achieved with those with smaller boobs. For a woman with smaller breasts it is easier to go on top and work that way, though many busty ladies also try this technique in order to provide their partner with the best feelings they can. Why not try switching positions and seeing what works best for you? It is a great way to exchange power, as being on top can show dominance for the man, while lying on his back and allowing the woman to control the pace will switch the roles around.
Whether this is a warm up act or the curtain call, you are bound to enjoy it, and some women find it to be a huge turn on as they feel like porn stars performing this act. Just make sure that, as you are getting closer, you let your partner know so they can prepare. Giving them a surprise like that might be enjoyable for you, but it's even better if your partner can get themselves ready to accept your offering in whichever way they see fit.