You won't always be at war in Crusader Kings 3. Rulers who are not at war regularly make money and some even get used to the idea of not fighting. You can take advantage of this by taking a small group of soldiers to attack a province for a small amount of loot and prestige and then return home.
This is a great way to immediately get gold that a province has acquired, which increases your ruler's prestige. The amount of Prestige you earn is one-for-one for the amount of gold your raid team brings back to your realm. To start a raid team, go to your military tab and make sure you have a rally point in a province you want to attack.
Click on the rally point, and it should take you directly to that province. The Rally Point tab at the lower right of your UI should give you the ability to breed local raiders. You can do this with a large army, but you generally want to use the option to Raise All As Raiders and go around the map. By hitting the Raise All as Raiders, all of your soldiers become raiders, and they go to major rally points. Better to have one, so have only one rally point in the province near the neutral location you want to reach.
Your army should appear as an icon of the traditional army, but they are raiders and they will only raid neutral locations they come across. The army should have three torches behind its main banner, which means it only raids. Place them on any neutral province available nearby and have them begin raiding. The raid on a place takes a few days. You can pause the game to investigate other areas to hit to see how much gold they get for their issues. The Raiding Army tab needs to be in place to see how much loot they get for attacking a specific location.
Once they're done, have them return to any neighboring province you own to receive all of the loot and fame they've earned. You can dissolve them at any time in the province you regulate to resume their local functions. If you are having raid issues, it is probably because the army you are using for raiding is too weak. You need a bigger Raid Party to successfully bring back the loot.
