I think that this question is going to be fundamentally difficult on two levels. The first is that if you are asking the question to those who have already read the book, it might be difficult to generate predictions of that which is already done. The second level of difficulty is that personal predictions are personal, and must be generated from the individual as they will change from individual to individual.
Yet, with this in mind, I think that you might be able to formulate some predictions based on what you have read so far. The first question that could lead to a prediction would be what do you think will turn out to be an obstacle for Lennie and George? Which person or condition might become a hurdle that could be too difficult to overcome? Another question that could turn into a prediction would be who do you think might help Lennie and George? The most basic prediction would be whether or not you think Lennie and George will accomplish their dream of the farm? I think that these questions could have answers that could turn into predictions for you on chapters 3 and 4.