After sacred worship services, it is good to fellowship with the saints; or, if necessary, to sequester oneself off in a place where the sermon (and the worship service) might be more fully-comprehended, and contemplated.
Sunday is God’s gift to His people. Enjoy the church’s worship services (first and foremost); but do not necessarily stop there. Take advantage of the church’s educational ministries, viz. Sunday School classes, catechism classes, new members’ classes, etc.
Do not feel badly about resting on Sunday. It is a good day for an afternoon nap.
Read good books. Pray. Relish your Savior.
As you do these things, you will be preparing yourself for the week ahead. If you fail to keep the Sabbath Day, you are essentially killing yourself, and cutting your life short.