My tip: Do not invest in ICOs. ICOs are not as much profitable these days compared to last year. If I were interested in a certain ICO(though extremely unlikely), I'd probably buy it after the distribution instead, as prices are sometimes lower after the coins/tokens are accepted on exchanges.
This is actually a very good suggestion and judging from the way ICOs have been lately during the bear trend and a lot of them trading far below their ICO price, I would even say it is a whole lot better waiting for the project of your choice to get listed first and then go ahead buying them when you feel they have bottomed enough and you are getting far below the ICO price.
However, for general knowledge, I guess the idea of doing due diligence on the team, checking if there is a product and looking at the vision is what is important the most, when investing in ICOs.