Safest way to grow bitcoins is either hold them or trade with altcoins
Though trading alt coins is not a really safe way of growing bitcoins but it is obviously one of the best ways of growing bitcoins because it can earn you some good profits everyday if you a good enough capital and enough knowledge about trading.
That's true not the safes way but a good way to multiply your coins and if you can manage to invest good capital in it then you can make profits even from small fluctuations on daily basis.
Daily trades requires experience or you can lose all your money... The best way for newbies is invest in a long therm when the subject is altcoins, just buy a bit of good projects and wait for the profit, it can take years however if the project is strong, you will profit.
Yeah it is good for starters or newbies to choose legit altcoin those legit altcoin is in top 20 in coinmarketcap the more market cap the more you have chance that you will not experience of loses that you can hold it for a long time because those altcoin are staying long in the market..