if I think personally a safe way to invest in cryptocurrency is :
1. the project runs according to the roadmap and whitepaper that has been made;
2. cryptocurrency that we invest in already has a product;
3. the team always updates about the progress that is happening in the project that we invest;
4. invest in project that are in the top 1-500 in coinmarketpcap (have a high volume);
5. the project we want to invest has been running for a long time (if I personally never invested in a new project), because investing in new project has a greater risk than we invest in old project.
Numbers 4 and 5 sums it up. High volume means a good profit though, you could say ahead you'll be having a better future with this coin. Next one is the the project than been running for a long time, a good one as well, because you don't have to deal with just a mere possibility anymore. They have been, and the project are on the way of making it more possible unlike to new ones that not even sure what might happen a long the run. Well, I just found these two a good reliability of safe investing.