I've always found, most weddings require you to wear something formal or very nearly.
One of the most important items to have as a guest at a wedding is a clean crisp white shirt.
By their very nature white shirts can go a bit yellow after several years of wear, if they're not of good quality. So now might be the time to invest in a fine two-fold cotton shirt.
If you already have the suit then maybe a new tie and handkerchief can have the effect of pepping up your outfit.
It is best not to match them however, it can show a lack of personal imagination.
Even if you find it wasn't required, it's easy to take off and put in your pocket, thus potential embarrassment avoided.
1. Buy a new white shirt so it always on-hand for your next event you're invited to.
2. Try wearing a tie you love and always have a handkerchief at hand. If you are not sure how to wear one, wear a white one.
3. Always get your suit cleaned and pressed.
4. When thinking about shoes, a black pair is usually the norm at any formal occasion. However, if you're feeling confident you can experiment with a brown or tan shoe, which can add some personality to your outfit.