I used to do this when I started out, and it worked ok. I would buy almost every coin on poloniex, maybe .01 worth of each, and then start setting orders. If the coin goes up 1000%, I already have an open order to sell 10% of what I bought. Then another 10% if it goes up again.
The reason I did that is because I didn't know much about crypto, so I was trusting that poloniex had chosen some of the better coins. I did avoid some like BALLS, or ones that were too expensive like SYNC. So I made a little money that way, but then I started researching, googling, and reading hundreds of pages of information here at bitcointalk. You can't believe anything that one person says, especially about an altcoin, so you have to keep digging until you get a bigger picture of what's real and what is lies.
So I started selling my coins that seemed to be outright scams - URO, BCN, anything with huge premine or false promises.
Then I started selling the coins that are just clones or have nothing special to offer. But I waited until I could sell them for more than I paid.
I still have some of those randomly-bought coins, still waiting for the price to be more than what I paid. Some of them will probably never get there, and some of them will probably be delisted. But it will only be .01btc for each coin, while I have already made an overall profit on other coins.
My "buy everything strategy" got me some coins that I am still holding, for example I bought Stellar at 400, 600, and 700, and now it's selling for 1800. I bought Opal for 899, and now it's over 3000. I bought some Storj for 4000 and 5000, and now it's over 10,000. I bought Dnotes at 1400, and now it's 4000.
But I also bought some Altcoin Herald for 3000, and now it's 100. (I did sell some for 4900, but I still have some).
So, without being able to see the future, how can we buy more of the good ones and less of the bad ones?
#1, try not to buy high unless you're really sure the price will never drop again. If you think a coin is selling for a good price today, then obviously it would be an even better price if it was a little cheaper. Put in an order for less than market, and wait. Have patience. And seriously, don't pay the ask unless you can admit to yourself that you're afraid nobody will fill your bid. Emotion drives many traders; they sell because they're scared, and they buy because they're excited. You want to be the calm person, buying from the scared people and selling to the excited people.
So find a good coin with solid fundamentals, no huge premine, no trillions of coins floating around, with a good name and good reputation. And then look at the charts - has it been cheaper recently? Is it on a sharp upward spike that you've already missed out on? Maybe wait. Maybe it will keep going higher and maybe it is a good buy anyway, but there are plenty of other coins that are currently cheap that might be better buys today.
Thanks for your advices man !