It was very simple, there was no SEC and insider trading was legal. He is known to mention after 1929 (probably after SEC was created) that rules of the game have changed dramatically. It is known he could not make any money in his later years after 1929 windfall. Plus, it is a bit of mystery what happened to 100mil he made shorting 1929 crash.
No internet, no options, no volatility indexes, no up-tick rule, no futures, no auditing of financial statements, no financial regulators, basically every man/woman for him/herself and anything goes!
Market was much less efficient in those days. Making money must have been easy for floor traders and MMs who could actually watch the floor brokers representing big money, and jump in along with their orders to scalp profits. And then you had a whole other layer to the game where whales like Livermore would trade off inside info, and manipulate prices to trap other players. The basics of trading haven't changed, though. Much deeper electronic markets means edges are narrower and opportunities vanish more quickly, but you can throw far more size at them and get in and out with a click. Buy in a bull, sell in a bear, pay attention to general conditions and scalp moves created by big money.
Back in the days Curb market was actually outside on the street (AMEX) and people in the building would yell to the traders on the outside curb prices etc.. Inside NYSE you would have posts with pegs to hang your hats. Pricing was displayed with mechanical indicators manned by employees., and to get a traders attention they would flap the price indicator to make a sound in order to get the attention of the floor.
Then 1950s you had the Univacs and IBM 700 series computers, people would look for the best vacuum tubes on the market to cut trading times. The hottest tubes with the best grids were gold.
Let's look beyond 100 years, here ya go.. https://www.investopedia.com/articles/07/stock-exchange-history.asp