I don't think that someone can tell a 100% secure and accurate cryptocurrency buying and trading strategy, because it simply does not exist, but there are some steps that can bring you closer to some progress:
1. Research the cryptocurrencies you want to invest in.
2. Find out at least 5 coins that you would like to invest in (diversifying your wallet is one of the major rules of successful trading).
3. Figure out the exchanges you can buy cryptocurrencies from (there are many of them but the rates change frequently, so check the rates to pick up the most profitable option).
4. Buy the cryptocurrencies and store in a secure wallet (selecting a secure wallet is also important, because some of them may be scam willing to steal your funds).
5. Store and wait.
Patience is one of the most important points here, because you have to know that you won't get rich overnight. So be patient, don't get disappointed when the prices fall, just follow all of the updates and trade whenever you think you will get some profit. And, of course, never stop researching!
Good luck!