The bad news is that it's nearly a sure thing that the market will crash one of these days -- perhaps in a year or two, or perhaps tomorrow. The good news is that you can take some steps now to prepare for a crash, and you can have a plan in place for what you'll do when a crash happens.
In general, it can be good to have no more than 10% of your overall net worth in cash for investments.
It's not enough to have a pile of cash to spend when the market crashes if you end up having no idea what to buy. So build and maintain a stock watch list. Start by jotting down the names of companies you read or hear about that seem like promising investments.
Another thing you can do if you're anticipating a market crash is to include a bunch of defensive stocks in your portfolio, as they tend to get less punished during a market downturn.
Market crashes present great shopping opportunities for those who are ready for them.