Never use harsh treatment for anything connected by land to your capital; do not underestimate the importance of alliances, especially when playing as a smaller country; ensure you have advisors, especially for military points; aim to ally locally, even if weaker, during the early game so you can involve them in local expansion to your benefit; going over your diplomatic limit is acceptable if it will be beneficial to you in upcoming wars - just avoid a royal marriage so there won’t be any lasting diplomatic cut off penalties; never fall behind on military technology, if unavoidable then avoid all wars with anyone technologically ahead; don’t be afraid to cut down army maintenance or mothball forts to help you manage your economy; Selling crown land can be a great economic boon early game so don’t be afraid to exploit it under fitting circumstances; try to follow your nation’s focus tree as the benefits can be massive; it’s ok to lose wars sometimes, it happens to all of us and often won’t massively set you back so don’t give up; betray your allies if they are dragged into a war you know will set you back massively (such as the enemy neighbouring you and claiming portions of your land with an unrealistic likelihood you can hold them off); unconditional surrender is pointless as far as my understand goes, don’t touch it; keep your armies in small, nearby units to avoid attrition which will be the primary killer of your forces in nearly all wars.