In his book on the Army of Flanders, Geoffrey Parker explains that about half of the Army was at any one time dispersed across dozens of garrisons throughout the Low Countries, and that they fought an almost guerrilla conflict with neighboring garrisons, and that these skirmishes demanded greater experience than large scale battlefield action.
Do we have any sources on what these raids and skirmishes would have looked like in terms of tactics? i.e. how to form up for an attack, setting up ambushes, etc?
A reply to /u/dandan_noodles
I can't find any mention of raids and skirmishes from the Eighty Years' War, but there are mentions of this in Mortimer's Eyewitness Account of the Thirty Years' War. One example comes from the account of Colonel Augustin von Frisch, serving the Imperial army and eventually surviving the entire Thirty Years' War. He was nicknamed "the tall rascal" by Pappenheim.
.... to forestall an enemy attack on the village of Altkirch; reaching there in time he forced two successive larger enemy patrols to surrender by allowing them to be admitted through one of the gates which, when closed, left them boxed in between the inner and outer gates under the guns of his concealed soldiers. He captured some 80 men and their valuable horses, and was rewarded by the residents into the bargain.
Another example follows:
In 1637 he induced a garrison holding a strongly fortified church to surrender by convincing them that he had undermined the building and was about to blow it up, work which would in fact have taken six or seven days.
So these are truly highly-flexible, highly-uncertain raids, counter-raids, skirmishes, and patrols.