Need to make my legs stronger. I normally average around 15,000 steps a day. Today I hit 35,000, and my legs are sore, they always are. Any tips on making them more acceptable to an active job? (20,00

Need to make my legs stronger. I normally average around 15,000 steps a day. Today I hit 35,000, and my legs are sore, they always are. Any tips on making them more acceptable to an active job? (20,000 steps on an average day)