How do I know what is an appropriate amount to ask regarding a slip/fall accident in a business with an insurance company?

Compensation for your personal injury claim should include the medical bills, pain and suffering, and wage loss.
Compensation for the medical bills is straight reimbursement.  The medical reports will document tha nature and extent of your injury and will be used to determine compensation for pain and suffering which is an amount in addition to the medical bills.  Compensation for wage loss is straight reimbursement.
There isn't any mathematical formula for determining compensation for pain and suffering.  If you did not have any residual problems after completing treatment, I would ask for quadruple the medical bills for pain and suffering, but not expecting to get that.  That would be a starting point in settlement negotiations.  Since you had a broken bone, I would ask for considerably more than quadruple the medical bills, but again not expecting to get that.  The insurance company will respond with a much lower offer and you can continue negotiations to try to get them to increase their offer.  If you will need future treatment, that should be mentioned in your medical report and the estimate should be discounted to present value.  If you have residual problems from the knee injury or broken bone, that would be grounds for additional compensation for pain and suffering.
If you are dissatisfied with settlement offers from the insurance company, your only recourse is to reject the settlement offers and file a lawsuit against the business based on premises liability. (Depending on the facts that caused you to slip and fall, your lawsuit may be for negligence instead of premises liability).  Most likely, it would be premises liability.
If the case is NOT settled with the business' insurance carrier, your lawsuit against the business must be filed prior to the expiration of the applicable statute of limitations or you will lose your rights forever in the matter.