The most profitable way I have found personally to invest is to find the right advisor. They all get paid, one way or the other. Here are the 2 that I pay for, each about $50 per year: Paul Mampilly's Profits Unlimited and The Motley Fool's Stock Advisor. These are the low cost advisory letters from each of those services. They give you the stocks to buy, and they tell you when to sell those stocks. Both are key to profitable investing. They have other advisories that cost upwards of $5K per year, but you don't need those. They give you at least 1 new stock pick per month, plus their entire portfolio of already recommended stocks. Buy and hold is the order of the day for 1-3 years at a MINIMUM because stocks go up AND stocks go down, much like the price of diesel pickup trucks.
In August of 2009, no one wanted diesel pickups and I bought my 2008 long bed crew cab LT2 for $22.6K, way less than the original purchaser paid just 6 months previously. The key thing here is that you BUY when prices are LOW, then wait until prices are HIGH and then SELL. There will likely be several ups and downs during this time. You BUY stocks when no one else wants to keep their shares and prices are low or companies with significant potential are starting to grow. The key thing is to buy GOOD stocks, and these advisors have proven that overall, they outpace the market something near 4X over a number of years. And don't buy ANY investment that you don't thoroughly understand. I don't understand Bitcoin or other such investments, and although I understand the trading strategy of options, I don't invest in those either.
If you don't want individual stocks, post #8 is great advice. This ETF is an S&P 500 index fund. Any similar fund is a great, no-brainer, low-cost investment in 500 huge, profitable companies, not likely to go broke and highly likely to be profitable for years in the future. Warren Buffet says he told his wife that when he dies, that's exactly what she should do, buy the S&P 500 index and don't look back. 15 % of your income each payday is a great way to start, and if you don't have 15%, try 5% this year, 6% next, 7% ... You get the idea.
Today is a pretty good day in the market. I'm up $94K so far. I've had days where I'm up $125K, and had down days of $175K. When you have those down days, you just have to remember that tomorrow will be better, and if not tomorrow, the next day or the next. Just look at the stock market indexes over time. The trend is ALWAYS UP. The trend is NEVER down. Dips for sure, but not the trend. You just have to wait out the dips until the trend continues.
Get started in investing, keep it up, don't sell when the market is down and you will accumulate wealth you never thought you would have.
