Do nothing out of selfish ambition or vain conceit, but in humility consider others better than yourselves. Each should look not only to their own interests, but also to the interests of others. Your attitude should be the same as that of Christ Jesus.
If you feel like you've let your behavior slide a little bit, and you're just not being as considerate as you once were, than by all means, try to get back to the way you used to be. It happens in most long term marriages, each person starts to get a little more at ease and let a little more of themselves out, sometimes that's not always a good thing. If you've both begun to do that, you may want to discuss the situation and both promise to try and do better. If the two of you can talk about these issues calmly and both agree to try and cut out the behaviors that bug your partner the most, things can be better almost immediately.
When it comes to learning how to be a sweet wife there is no one size fits all solution but there are two things you can keep in mind. One, treat your husband the way you want him to treat you. That's good relationship 101. If you wouldn't like him to not say 'please' or 'thank you' than don't do that to him. If you wouldn't like it if he didn't call if he was going to be late, than don't do that to him. You get the point. Treat him the way you'd like him to treat you.
Second, try to respect his wishes. For example, even if you wouldn't care about a certain thing, like calling if you're going to be late, if you know he does care about that than respect it. Each person will have their own unique attitudes about all kinds of situations, sometimes the two of you will agree on these attitudes, sometimes you won't. That's ok, just try as much as possible to respect his ideas.
Of course, you don't need to, and shouldn't, completely rearrange your whole personality to accommodate your husbands likes and dislikes, but a few compromises such as I explained above, really won't hurt anything. In fact, it can also make you a better and more considerate person too. You can both be happy.
Learning how to be a sweet wife isn't hard and it isn't rocket science. For the most part it's just about being considerate and affectionate. It's not about doing everything that your husband wants you to do or being at his beck and call, that's a doormat, not a wife.