since bitcointalk is the most popular forum about cryptocurrencies and everything cryptocurrency related
you have come to the right place to promote both (if your telegram channel has anything to do with the crypta,that is)
the simplest and the cheapest way is to create a topic in the corresponding forum section
for ICOs and bounty campaigns would be:
https://bitcointalk.org/index.php?board=197.0 and
https://bitcointalk.org/index.php?board=238.0Telegram channels can be advertised in either:
https://bitcointalk.org/index.php?board=198.0 or
https://bitcointalk.org/index.php?board=84.0 ,depending on the content of the channel
you can run a signature campaign for your ICO: a random example:
https://bitcointalk.org/index.php?topic=2521066.0and the list of signature campaigns:
https://bitcointalk.org/index.php?topic=615953.0you can buy ads here,participating in the auction :https://bitcointalk.org/index.php?topic=2047814.0
if you want more options and you have adequate resources to do so,
you can use Google Adwords or you can buy ad spaces at one of the bitcoin ad networks such as
https://a-ads.com/ ,
https://mellowads.com etc.
another good option would be writing or buying an article, sending it to the cryptonews portals such as
https://www.coindesk.com/ ,
https://cointelegraph.com/ etc.
maybe even posting it here under the news section:
https://bitcointalk.org/index.php?board=77.0 pay attention to SMM (social media marketing) it is a great tool to advertise your project as well:
reddit
https://www.reddit.com/r/Bitcoin/ and twitter are both great sources of cryptocurrency enthusiasts
while facebook is not that friendly to anything bitcoin related in terms of advertising,but you can try there too:
https://www.facebook.com/there are many more ways to advertise your project,with various efficiency and for different types of budgets,for example:
free tokens giveaways,purchasing views at paid-to-click bitcoin sites,even the so called black marketing
but I think the ones I mentioned above should be enough for you for the time being
good luck with your project!