The first thing you need to do is find a project that excites you and that serves your needs. There are several aspects to consider:
Currency or Project
ICOs can either be launching a new cryptocurrency or funding a new startup. Usually each one will offer investors a different payoff for their investment. A cryptocurrency ICO, is looking to launch a new currency into the market, hoping that it will catch on as has happened with Ethereum or Bitcoin. However, this is quite difficult to do if there is not some inherent added value in the new currency like the platform that Ethereum developed for example. A project ICO is similar to a startup. Here you should consider whether the project is providing a solution the market needs, as well as if it is something useful to you as you will often receive tokens for the service or product.
It is important to understand what would be the potential value of the token or currency you receive after the ICO phase. Raising money just for the sake of hoping to create the next Bitcoin is not enough. Creation of a new platform or ecosystem around a new currency, like Ethereum did, would be an example of a currency with solid long-term potential.
Capped or Uncapped
A capped ICO can decide to release a definite number of tokens or coins. A credible ICO will also lay out the amount to be released, the pace, and the end date of distribution. An uncapped ICO won’t limit the number of tokens released but might predefine the amount of time the tokens will be available for purchase. These considerations have a significant influence on supply and demand, how the ICO will run, and how the coin or token will behave later on.
Fixed or flexible price
Some ICOs will set a fixed price of purchase that will not change regardless of the amount sold or the time frame. However, other ICOs might adjust the price of their tokens, either providing discounts at certain times, or raising prices as funding rises. In this case, it is important to consider when in the ICOs process you are getting in.