What are the best long term, low risk investing opportunities, on the order of ~USD 5,000

My short term invest strategies in the stock market tend to be a bit more quick 6month - 1 year trade. I'll find shares that I think show potential in the coming fiscal year, and then cash out when the hit +/- 10% of their value (varies based on stock).

This, of course, is a higher risk approach and I only want it to constitute 50% of my portfolio.

What do I do with the other 50% of my money (currently around 5,000 USD) that's lower risk and has potential for long term growth? Are index funds the best option? Anything else?

I'm still a pretty noob investor, so would love to get your thoughts.

Thanks!