Having social media accounts and boosting posts might work, and also using Airdrop/Bounty to build your community on Telegram are pretty much a must-do.
No, it's not. I know some project that doesn't do any of those airdrop/bounty and they still have a huge community. Instead of paying fake users to join your channel, it is better to use that funds to promote/shill on various ICO/IEO/Crypto review channels. That's powerful marketing, way more powerful than requesting people to wear your tag and join / spam on various groups.