Welcome Jennifer! Yes, a pair of slacks and a nice blouse is ok for Mass. When you go, the best thing is to seat yourself where you can observe what is going on, that is where you can see the altar, watch the posture of the people,etc. Most parishes have a booklet which has the Mass printed so you can follow, you can ask one of the ushers to assist you. Most people refer to this booklet as a missalette. Just do what everyone else does, or you may just sit and observe. Since you are not Catholic, we ask that you not go up for Communion, but you may stay in your seat. No one will pay attention, not everyone goes up for Communion. Some people go up with their arms crossed to just receive a blessing, but this is not really approved and many parishes do not observe this custom, so I would advise you just stay seated to avoid confusion.
There is not much socializing done in a Catholic Church, so don’t feel as if people are not friendly. After Mass is when many parishes will have a coffee and donuts time, but at first you will notice the difference from your usual non-denominational churches which have plenty of greeters. People get to know each other usually by participating in parish activities and small groups. Take notice of these things in the bulletin.
The Mass is structured, and the basic parts do not change. There are 3 scripture readings and a psalm, which is usually sung, and you will notice that the prayers and responses have a lot of scripture in them. There are two basic parts of the Mass: the Liturgy of the Word, in which scripture is read and the priest or deacon preaches a short homily based on the readings, and the Liturgy of the Eucharist in which the priest prays the Eucharistic prayers and consecrates the bread and wine to become the Body and Blood of Jesus, and Holy Communion is distributed. Depending on the parish and the formality of the Mass, there may be contemporary songs, traditional hymns, chanting, various instruments, no two parishes or Masses are alike in this.
The best thing is to just relax and observe and go to enough Masses to become familiar with it, and listen carefully to the prayers. There is a lot of praying. There should be cards or booklets to assist you in the pews. You also will notice various artwork, statues of Jesus and Saints, stained glass windows depicting biblical scenes, and of course a Crucifix. We never worship these objects. They are there to remind us of Christ and teach us and inspire us to live holy lives. We use all of our senses in our worship, from crossing ourselves with holy water to remind us of our Baptism, to hearing beautiful music, seeing the beautiful artwork, often smelling incense and flowers, and tasting the Eucharist. Everything is there to experience God more fully in our worship.
This is long and very basic, but I hope you enjoy your experience. Liturgical worship is quite different from the worship style in many Protestant churches. I have always found peace and the feeling of being safe in the rhythms and familiarity of the rituals, like a small child does when his parents read him a bedtime story. I know God is there and I am safe at home, yet it never grows stale. God bless you.
As long as you are dressed modestly, (no skimpy stuff), you’ll be okay 
I am a newly baptized Catholic, so please feel free to message me with any questions!