Long term investments should be looked at very carefully. Read up on the currency, not just their site and whitepaper, to gauge how the community feels about it. If a product starts out great and the community starts seeing that they aren't delivering on promises then they will jump ship.

Some things I always ask myself is 1) Can they deliver given their team, current state of blockchain and the current adoption rate of blockchain technologies? 2) If they are post ICO, are they delivering on the milestones promised? 3) Is their product/service something I believe in and understand? That last one is key in a long term investment because when the market dips, or that specific currency, you'll be able to gauge different factors and determine whether to hold or to sell.

Good luck!