Yes, there are a few things to address, I would touch base with an imaam prior to your visit. Yes, it is great to have non-Muslims to visit if they are truly curious and will show earnest attention to learn.
What you should consider on what to wear:
1.Pants, you can wear shorts but they have to be past the knees...wear pants to be safe
2.No gold rings neither necklaces. If you have piercings, take them off. If you truly convert, you wont need such jewelry, definitely wont have piercings and only wear a SILVER ring if your married.
3.Descent size shirt in case you commit to a prayer, nothing too short nor too tight to where your back is exposed when bowing.
4.If your a female or taking a female, you/your female friend can ONLY go on the women side. ITS IMPORTANT TO ASK Imaam first because the potential sister will need to cover her head with a scarf, also known as hijaab. Women dress code slightly different and MUST NOT EXPOSE her body only to a minimum such as hands and face. NO SKIRTS,DRESSES or tight clothing.
Its important to let the Imaam know because they could just give you a chair, you can sit at the side if not in the back and watch the prayer. After wards, the Imaam would love to explain what you saw. He would give you information such as books,web links, ask for your email and provide further information to get you started on praying if your that interested. Most of the time after Juma, there are evening gathering that teach and bring awareness to spread good deeds to other brothers and sisters.
Again, call first, make sure the masjid is a good sized establishment to get to learn from vast majority instead of a small cluster. Hope this helps and hope you do find Islam to be as fantastic as we do.
Peace be with you,
Yahya