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.
In my own point of view, if you really wanted to invest safely in cryptocurrency, you should avoid investing in new projects because you cannot say if you will receive a reward from it or if it is legitimate. You should be investing your money in coins that has a potential to increased it's value for you to gain profit like bitcoin, ethereum, litecoin, ripple and etc.