As others have said, just play in release order. The story is wild and wacky at times, but MGS1 is very straightforward, and MGS2 only really gets confusing if you're trying to understand the meta-narrative (you can always watch the SuperBunnyhop video for that if you want). MGS3 is also super fun and the most inward-focused of the original three, so lots of story and lore abounds for characters from the last two games.
As others have said, just play in release order. The story is wild and wacky at times, but MGS1 is very straightforward, and MGS2 only really gets confusing if you're trying to understand the meta-narrative (you can always watch the SuperBunnyhop video for that if you want). MGS3 is also super fun and the most inward-focused of the original three, so lots of story and lore abounds for characters from the last two games.