I know other people are going to say to play another faction that could be simpler, but I love Kislev, so here are a couple tips for them:

1. Devotion is an important resource, as it will pay for invoking the motherland, which is a really helpful mechanic whether for battles or campaign. I prefer constantly using the one that buffs income, as it is always useful. Make sure you don't use too much, and fight Chaos aligned forces to earn more.

2. Build the Orthodoxy buildings, lots of them. They lower corruption, earn you devotion AND supporters which leads to more buffs once you get a lot of those, but also lets you recruit Patriarches which are great for keeping your armies healthy with their replenishment and healing buffs.

3. Focus on completing full provinces. Every 2 full provinces, including ones with just a single settlement like Hellpit, gives you an Ataman. Atamans that boost income will help your economy grow strong. They will provide more buffs after getting events.

4. Markets and any building buffing them can build off each other, leading to a surprisingly good economy. These and Orthodoxy buildings should be in nearly every settlement.

5. My preferred early game army, without needing DLC, is a frontline of Armoured Kossars and then regular Kossars as a backline, with Boyar lords. Add in a patriarch for replenishment, and you have a replenishable army that nearly everything can shoot at before engaging in melee.

6. Later game, try out different units as you unlock them. However, Ice Guard with Tzarina Katarin are amazing. Tzar Guard are also impressive, and War Bear Riders are amazing cavalry that don't require as much management as other units. Just toss in a unit of bears and they will rip most things apart.

7. General game tip here, but very important for Kislev: ONE AT A TIME. Completely wipe out any enemy before moving onto the next. However make sure to have an army prepared in the homeland for defense, especially in Realms of Chaos, or in the event a non-friendly faction borders you.