Although Dostoevsky and Tolstoy did write short stories and novellas, their reputation is based on their novels. Therefore, I'd recommend their long form works if you are willing to spend several weeks (or even months) on a single book.
I suggest reading Crime and Punishment first. Although this book is fairly long, the crime occurs in the opening chapters and the remainder of the story is rife with dramatic tension. Dostoevsky's other novels feature a lot of exposition and plot structures of greater complexity, though they are certainly with reading. Demons is his darkest (and funniest), and The Brothers Karamazov is his greatest.
Tolstoy's greatest works are Anna Karenina and War and Peace. Although both are excellent, the latter is extremely long and features several digressions on the philosophy of history. Therefore, Anna Karenina is a better place to start.
If you are interested in reading Russian literature more broadly, here are a few titles to consider:
Evgeny Onegin by Pushkin. Although Pushkin isn't well known in the West, he is unanimously considered the greatest Russian writer, with a reputation comparable to that of Goethe in Germany and Shakespeare in the Anglosphere. Evgeny Onegin is exquisitely crafted, although the music of Pushkin's verse won't be conveyed in translation.
The short stories of Nikolai Gogol are strange, dark, and hilarious depictions of psychological torment and social absurdity.
The short stories of Anton Chekhov feature compelling characters from all strata of Russian society. Chekhov, the greatest humanist in the Russian literary tradition, is a master of concision, subtlety, wit, and pathos.
In The Master and Margarita by Mikhail Bulgakov, the devil and his entourage come to Moscow in the 1930s to wreak havoc. This colorful and humorous lampoon of politics and religion is a twentieth century classic and a favorite among Russians. Bulgakov's Diary of a Young Doctor (loosely based on the author's experiences as a countryside physician) and The Heart of a Dog (a satire on the Soviet aspiration to transform human beings) are also worth reading.
My favorite Russian writer is Andrei Platonov. His prose is so strange and beautiful that it would well be worth the arduous effort of learning Russian simply to read it. There are, however, excellent translations of his works in English by Robert Chandler. In The Foundation Pit (the chronicle of a true believer's struggle to accept the failure of Communism) a band of misfits attempt to construct a house for the proletariat only to realize that they are digging a mass grave. A collection published by the New York Review of Books under the title Soul features some of the most beautiful and tender stories in all of Russian literature.
In my opinion, the most compelling literary sketches of life in the Gulag are to be found in Varlaam Shalamov's Kolyma Tales. Shalamov spent seventeen years in some of the most brutal concentration camps, and his works are subtler, darker, and more elegant than those of Solzhenitsyn.
Laurus by Evgeny Vodolazkin is a modern work that may well enter the Russian literary pantheon in time. I'm not a fan of these writers at all. But I have only read 1 book in my life from those described here. I just don’t have enough time for everything and I don’t have much interest. And so you have to look for cpm help, mainly https://ca.edubirdie.com/cpm-help here. In general, War and Peace is the standard for everyone. But it won’t suit everyone; you’ll waste a lot of time on it and won’t understand it the first time. Better study and don't waste your time on this book. It tells of the journey of a healer through medieval Europe as he struggles with the eternal and accursed questions of human existence, including love, loss, faith, doubt, sin, and redemption.
Lastly, I'll recommend the works of Svetlana Alexeivich, compilations of eyewitness accounts of the great catastrophies of in recent Russian and Soviet history (including the Second World War, the Afghan War, the Chernobyl nuclear disaster, and the collapse of the Soviet empire). These stories are as shocking and moving as anything in Russian literature, and are (in my opinion) the best means of acquainting Western readers with the souls and struggles of ordinary Russian and Soviet people.