Safest long term investment is to dollar cost average into an index ETF or fund. Don't look at it, don't trade it, just put into it while you're earning. IRA, Roth, 401k or other tax deferred investments is the best. Max them out if you can. Yeah, you don't get rich overnight, but over the long haul you'll most likely get 7-9% growth a year. Also make sure they are very low cost funds. You don't want some fund manager skimming 1% or more off your portfolio every year. That'll kill you in the long run. I've built a nice nest egg over the years that way. Amazing how much it grows once real money starts accumulating in there. Just to give you an idea, I had a small 401k back in '95 that rolled into an IRA. It was about $2,300 in 1995. Today that account is worth about $30,000. I haven't ever touched it. Just let it sit there and grow. Just think, instead of buying a new car back in '95 if someone put away $20k (about the cost of a new mustang GT, SUV or Trans Am at the time). You'd have $260,000 today. That's an even better return than if you had purchased a nice 455 SD back then.
You can't beat compounding interest.
As far as options, individual stocks and other less diverse investments? Well lets just say your odds are probably better going to Vegas with your money. Not that you can't win, and if you are both lucky and well researched you may even beat Vegas odds. But I've found repeatedly for every winner I pick I also seem to hit a loser or two. I might make 100% on one stock and lose 50% on another. In the end I'm making money on my individual stock investments, but I'm making a lot more on my index funds.