Sex advice

I'm sure most of us are grown here so here I go, every time I 'ride' my SO I feel like I'm not doing it right. I look at him and he looks like he's enjoying it, but I feel like I'm not giving him enough pleasure. He told me awhile back 'just move your ass' and I just can't. I'm not a heavy person either, but my legs get extremely tired real quick and I don't have a huge ass but I'm weight training so it's getting bigger. Could it maybe be because my ass isn't that big to just move it or is it just me? Should I practice moving my ass when I'm alone? He's a great hardworking caring and loving husband so I want to make sure he's happy and he's getting pleasure, I have our house clean and cook for him so I know sex isn't the most important but it's definitely up there. Don't judge or put rude comments, I'm just asking for advice.