How should I invest $1000 on a monthly basis? I am a greenhorn investor and do not really have time to go through financial analysis for companies.?

You can start with robo advisor as well as regular savings plan.

1k on a monthly basis. Robo advisors are a good option. Just take note of the costs. Different advisors have different methodology. Choose your preference

If u want higher returns then it is advisor to learn to research on a company

Think alot of people face the same problem: no time to research.

Here are a few options you can consider.

1) Robo-advisors such as Stashaway/Autowealth. They do everything for you including rebalancing so it's really a set and forget thing but their fees are generally higher than if you DIY.

2) Buy into low cost global index etf like VOO that tracks the S&P500 index. Definitely cheaper than robos but you have to do the rebalancing of the portfolio yourself.

All the best in your journey!

Go for low cost ETF that track global stock like VT, VWRA, IWDA.
If u think this is still take times, go for robo advisor which charge slightly higher cost.