Knowledge of prehistorical medicine is limited, because of time and lack of records. However, we can draw assumptions from burial sites and also from some existing traditional cultures [drawing more from cultures without a written system, which would be similar to prehistoric humans].

Which ailments were common among prehistoric humans?

A lot of people had illnesses suggestive of heavy repetitive labour, like osteoarthritis and spinal issues. Fractured bones were also common - and it largely seems prehistoric communities were not all skilled at setting bones - they had some knowledge of the anatomy by how body parts were arranged at burial, but bodies have also been found to have badly-set bones. Also infections and viruses, which were compounded by lack of knowledge regarding hygiene.

However, due to the higher mortality rate back then, epidemics tended to burn out quicker.

medical techniques and / or rituals

Herbal medicine would be the main one. Tonics and ointments would be made from various local plants and applied to wounds, or be ingested.

Also, the use of medicine men/shaman/spiritual person, due to the belief that illness was created by evil spirits. In many older cultures, there is a belief that everything happens for a reason [i.e. there are no accidents] so various rituals would be used to ward off bad spirits and to remove said spirits from a person.

There is evidence of trepanning - drilling holes and shapes into a person's skull, or scraping the skull using a flint. Most likely used in an attempt to remove evil spirits and to relieve things like headaches.

A good starting article: http://www.medicalnewstoday.com/info/medicine/prehistoric-medicine.php

Older article, but has some very good information: Trepanation from the Palaeolithic to the Internet

hi! it may be worth x-posting this to /r/AskAnthropology and /r/AskScience for additional information