Do your research first, and invest in 1 or 2 altcoins that you have a gut feeling, and you believe in the whole project to be a success. I have recently Invested in IOTA, but only after reading hundreds of pages and posts about it. I am holding it long term, and slowly buying some more.
Another, short term investment I recently made are on two coins. Mysterium, and Quantum Resistant Ledger. They are new addition altcoins of June, and I hope they will rise 300-500% in near future, so I can seel them and buy more IOTA :)
Good luck, and the best advice I can give you is to invest in coins you like, but never get emotional about them