Right: conservative. Policy designed to preserve corporate interests and wealthy elite. Often masquerading as “looking after the middle class” - when really at best they get some trickle down benefits. Selfishly You should be right leaning if you are a significant owner of capital or have a very high chance of that (they will convince you that everyone has this chance).
Left: Progressive (in that it looks to reform the existing structure). Policy design to assist the working class (wage earners). It typically looks to take from corporates/wealthy elite and redistribute. Selfishly You should be left leaning if you don’t own significant capital and derive most of your income from wages.
Unselfishly you should err on the side of the left as it is aiming for a “greater good”.