There are many schools of thought on investment.

Here's some general tips:

Diversify, but not too much. You want to avoid having all your eggs in one basket. However, each additional basket gives less value for diversification purposes, because the chances of many independent investments failing together is low. And when you do get a broad failure, being highly diversified doesn't help much anyway, since all asset classes are affected.

Invest in things that you are familiar with and understand. By limiting yourself to between 6 and 12 different and unrelated investments, could can benefit from your own knowledge while still not having too much risk from any one asset.

Don't spend too much time on your investing. The benefit of investing is putting your capital to work, without a lot of labour. Dedicate a few days every six months to reviewing/researching your investments.

If you don't have much to invest, don't bother with any of this. Just put your money in the highest interest savings account you can find until it is a large enough some to be worth investing.