Dont be afraid to laugh. Sometimes it makes me laugh when my husband spanks me really hard. Yes it hurts but it makes me so giddy that sometimes I just can't help but laugh. Try not to make is too corny like what you often see in bondage porn , nobody can take that seriously in real life. No cop uniiforms with him saying I need to frisk you and put you in cuffs ma'am (unless that is what you want!). Try to incorporate it into your life instead of making it fake, it will be easier to take it seriously that way. For instance is there something you do that really annoys your husband? I know mine hates it when I do not have the dishes done and will often punish me for this. So if there is something that you know irks him you guys can use that as an excuse to punish you. Let's say your husband is annoyed like mine that the kitchen is filthy. He comes home and there is a mess. He tells you to apologize. He tells you that you need to be punished so you will remember next time to keep things clean. He bends you over the sink of dirty dishes while spanking you, that way you are reminded the whole time it is happening why you are being punished. Then maybe he tells you he is not happy with you and you need to make it up to him so he puts a collar around your neck and leads you into the bedroom by it. When there he tells you he loves you and is doing this for your own good to make you behave better. He then proceeds to put you on your knees and have you service him until he is satisfied. Then he makes you apologize again and if he believes you and you deserve it he may satisfy you back.
I find these types of situations feel much less silly than him just spanking me saying bad girl bad girl (although that is fun too).

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Its one of those things that you have to get used to, at first all you can do is laugh at him but he will get fusterated and just spank you a little harder. My suggestion is start off slow, then work your way to higher level.

Have to agree with not being afraid to laugh, since sex should be fun. Overall, just start slow and work your way to a point where you're comfortable. The easiest is handcuffs or blindfolds, and both can work to as serious a level as you want to take it.