Seems simple enough, but it's common to find two different insurers charging very different prices for the same or very similar products. Car insurance in particular can be sensitive to how many years you have been driving - a new driver may be better off with one company, and a very experienced driver may be better off with another. Some insurance companies offer discounts when you combine insurances, so it pays to check this as well.
Consider paying by the year instead of by the month if you can afford to. You often get charged extra for paying by the month, and your bank may charge extra again for a direct debit from your account. If you do decide to do this, be sure to save the 'extra' money that you would otherwise have been spending on insurance each month by transferring it into a special savings account, or you will just spend it on something else instead.