Besides fighting they were mostly trying to get by, care for their families - which in many cases followed the army -, and enjoyed the spoils of war, i.e. rape and plunder.

For a first hand account see the diary by the German mercenary in the 30 years war Peter Hagendorf. I do not think it is translated to English in its entirety, but I have read parts of it translated. I will try to remember where. If you can read German there are several sources online, e.g. this ph.d.

In the diary Peter describes that his motivation was to get a means of living.