None of us can predict when things are going to happen (good or bad). We don't know how long the good periods will last (this is the time to be saving) and we certainly don't know when Murphy's law is going to kick in to gear. That's why building an emergency fund is critical and this is much easier when Murphy isn't living with you.
What does this look like? This looks like setting money aside when money isn't needed for emergencies, repairs, purchasing of new equipment, and, generally speaking, when there's a little extra cash in the bank. The bigger question is how much should be put away? Partially this comes down to what keeps you up at night. If you sleep soundly knowing that you have 6 months worth of expenses in the bank, then go for it, but if a year or more calms your nerves a little better, then head in that direction.
What to remember: A finance professor once said to me: "investing shouldn't cause you to lose sleep at night". In other words, you have to decide what level of risk you feel comfortable with and what level of risk is acceptable for your company.