Suggested reading list of ML classics for beginner communists:

1. "Karl Marx" by V.I. Lenin

A very basic introduction to what is and isn't Marxism, as well as a brief introduction to the man himself.

https://www.marxists.org/archive/lenin/works/1914/granat/index.htm

2. "The Three Sources and Three Component Parts of Marxism" by V.I. Lenin

To become a Marxist isn't to memorize individual statements Marx made, but to understand his methods of analyzing society

https://www.marxists.org/archive/lenin/works/1913/mar/x01.htm

3. "Socialism: Utopian and Scientific" by F. Engels

Marx & Engels didn't come up with the ideas of socialism and communism, but they were the first to approach the topic from a scientific angle. This is a must-read for understanding scientific socialism.

https://www.marxists.org/archive/marx/works/1880/soc-utop/index.htm

4. "The German Ideology" (Chapter 1) by K. Marx & F. Engels

This is an introduction to historical materialism

https://www.marxists.org/archive/marx/works/1845/german-ideology/ch01a.htm

5. "Dialectical and Historical Materialism" by J.V. Stalin

This text breaks down dialectical & historical materialism into very plain language that's simple to understand. Tho presented a bit mechanically it's still good for gaining a basic understanding

https://www.marxists.org/reference/archive/stalin/works/1938/09.htm

6. "The State and Revolution" by V.I. Lenin

Very important work for understanding the fact that states exist because classes exist, and not the other way around. To create a stateless society, the material conditions that give rise to classes must go 1st

https://www.marxists.org/archive/lenin/works/1917/staterev/

7. The following texts by Lenin are on revisionism and reformism (right opportunism in general). These words are thrown around a lot, but they have very specific meanings:

"Marxism and Revisionism"
https://www.marxists.org/archive/lenin/works/1908/apr/03.htm

"Marxism and Reformism"
https://www.marxists.org/archive/lenin/works/1913/sep/12b.htm

8. On the other end of the spectrum, we have ultraleftism, which objectively enables right opportunism despite the rhetoric. Lenin gets into this in his work "'Left-Wing' Communism: an Infantile Disorder"

https://www.marxists.org/archive/lenin/works/1920/lwc/index.htm

9. Now to tie dialectics in with philosophy, we have two essential works by Chairman Mao Zedong, "On Practice" and "On Contradiction." If you only read one, read the latter.

On Practice
https://www.marxists.org/reference/archive/mao/selected-works/volume-1/mswv1_16.htm

On Contradiction
https://www.marxists.org/reference/archive/mao/selected-works/volume-1/mswv1_17.htm

10. Here's what I like to call the Sparknotes of Marxism-Leninism. "Foundations of Leninism" by Stalin is a great read that's short and simple.

http://www.marx2mao.com/Stalin/FL24.html

11. "History of the Communist Party of the Soviet Union - Short Course" is great not only for studying history, but also seeing how history repeats itself. The various trends of opportunism that the Bolsheviks struggled with are well and alive today.

https://www.marxists.org/reference/archive/stalin/works/1939/x01/

12. At some point, you should probably read Marx's Capital. It might seem intimidating at first, but you should get the hang of it. I suggest putting this off until you feel more comfortable with the rest of the basics.

https://www.marxists.org/archive/marx/works/1867-c1/

13. "Wages, Price, and Profit" by Karl Marx is a good introduction to concepts like the sale of labor power, surplus value, etc.

http://www.marx2mao.com/M&E/WPP65.html 

14. "Imperialism, the Highest Stage of Capitalism" is a very important work by Vladimir Lenin. Anti-imperialism is one of the greatest weak-points of western communists. "Leftism" w/o anti-imperialism is like a car without fuel - it won't get you anywhere

https://www.marxists.org/archive/lenin/works/1916/imp-hsc/

15. These three parts of Anti-Dühring by Engels get into Marxian philosophy, political economy, and socialism, respectively

I. https://www.marxists.org/archive/marx/works/1877/anti-duhring/ch13.htm

II. https://www.marxists.org/archive/marx/works/1877/anti-duhring/ch13.htm

III. https://www.marxists.org/archive/marx/works/1877/anti-duhring/ch23.htm

16. If you want to see how Marxist theory is applied in real-life situations, look at how Mao analyzes the class relations in China, which was a semi-feudal half colony at the time: https://www.marxists.org/reference/archive/mao/selected-works/volume-1/mswv1_1.htm

17. More works on right opportunism by Lenin:

I. The Proletarian Revolution and the Renegade Kautsky
https://www.marxists.org/archive/lenin/works/1918/prrk/index.htm

II. The Collapse of the Second International
https://www.marxists.org/archive/lenin/works/1915/csi/index.htm

18.

III. Opportunism, and the Collapse of the Second International
https://www.marxists.org/archive/lenin/works/1915/dec/x01.htm

IV. Imperialism and the Split in Socialism
https://www.marxists.org/archive/lenin/works/1916/oct/x01.htm

19. "On the Correct Handling of Contradictions Among the People" by Mao Zedong

This one is very important - the improper handling of contradictions results in unprincipled capitulation towards the right, or the breakdown of unity.

https://www.marxists.org/reference/archive/mao/selected-works/volume-5/mswv5_58.htm

20. I'll add more to this list as time goes by, but if you haven't studied this, now is a great time to smart. History and theory guide practice, & practice further develops theory. There is an utter disrespect for studying theory in the western left, and this needs to change

21. How could I forget this one? Since many people in the west who become disillusioned with capitalism and liberal democracy turn to anarchism, beginner communists should certainly check out Stalin's "Anarchism or Socialism?"

https://www.marxists.org/reference/archive/stalin/works/1906/12/x01.htm

22. "Critique of the Gotha Programme" by Karl Marx

Read this so you can understand why anarchists are wrong when they go "Karl Marx is against the dictatorship of the proletariat and called for abolishing the state immediately after revolution."

https://www.marxists.org/archive/marx/works/1875/gotha/