All depends on whether it’s a one off or a repeated variance. Also if it’s favourable or adverse If it’s significant or not
Then you need to review the possible reasons for it If it’s material you have paid more or less, why is that? Discounts, new suppliers, inflation etc You have used more or less materials Why is that? The materials are good or bad quality, your staff have worked more or less effectively with materials ie more waste or less And so on ..