If you suffered a first trimester miscarriage (and the majority of pregnancy losses occur in the first twelve weeks), your body will be able to finish the process of miscarriage by itself, and expel all relevant tissue from the uterus, in the vast majority of cases. You will need to watch out for signs of infection like sharp abdominal pains and fever. If you are simply not feeling right, and you are worried, you can contact your healthcare provider or go to the ER at any time. Fever, pain, vomiting, or your intuition telling you to be worried can all be signs that part of the tissue from your pregnancy remained inside your uterus. This needs immediate attention.
If, after your miscarriage, you feel physically OK, apart from some tiredness and weakness, you can call your doctor for an appointment at your convenience, to check if your uterus was cleaned out. You might also want to check when you can start trying to conceive again with your doctor, though it is generally safe to try to get pregnant again soon after a miscarriage (New study says conceiving soon after miscarriage is safe). When you are emotionally ready to try again, you are good to go.