A very common practice in scam coins is that of Premining. That is, the practice of privately mining a new coin before the public sale and/or release. In the most blatant example, a coin developer sets an extremely low mining difficulty level, mines a certain amount of the coin, and, after a certain amount of time, publicly announces the release. There are less obvious methods of achieving a prominent effect, such as a last-minute announcement of the launch through an obscure publication.
With the dawn of tokens anyone without programming skills has been able to issue scam tokens.
There are far too many scam tokens around to talk about them, always DYOR but, if I was to advise you, only trust bitcoin!
The premine scam was a common fashion in the early years, but for now at least as far as I can see it, it doesn't exist anymore as PoW is also quite out of fashion. One of the biggest yet successful premined coins was DASH, former Darkcoin. The developer mined a ton of coins for himself before getting others involved seriously in the process. If you recall how DASH exploded later on, the guy made tons of money.
But there are enough other ways to scam, actually endless ways you could say.