A call to action helps when there's only one (you're not pelting them with multiple things to do) and it's done in an effective, genuine way. If the call to action is on your end card scene, of course, you have to get your viewers that far to even see it. Try to get your retention rate to at least 50% by the end of the video by improving your intro hook and having engaging content that doesn't signal the end of the video before the 20 seconds. (like "in summary").
Don't always use like/'subscribe. transition into another related video and tell them to watch it. That will increase your session time and youtube will promote you more.