The best channels keep changing and testing their thumbnails and titles until they find the winning combination. You should strive to do the same.
This is one way of making A/B test. However, before starting you should figure out what is your goal CTR for the duration of the test. Let’s say the average CTR on your channel is 6%. This is on the lower side, and so you can set the CTR for 7%, as your median goal.
Length of the test: 10 days.
Prepare 2 main titles and 4 thumbnails (2 for each title), and make sure the combinations work well. If you want you can add one title and one thumbnail as your backup options.
The first combo. Remember, in the first 24h your video will be shown to your regular audience. Therefore, your CTR goal for the first 24h can be a bit higher than the median goal.
Check a video in an hour or two after publication. If the CTR is higher than your goal, keep it. Check in the morning again to ensure it is still okay.
If in the morning it’s dropped, use the second option of the thumbnail for the first title. Now give it 24 hours.
The second combo. If the following morning the CTR didn’t improved, it’s time for the second combination. Choose the second title and your third thumbnail. And give this combination 5-7 days.
If your CTR is lower than the median goal, change it to the second thumbnail.
If the CTR didn’t improve change to the second option for the first title, and give it 2 more days.
After the initial test, keep consequently changing thumbnails and titles on a regular weekly basis.
Keep results of your tests in a dedicated table, where you mark the results and changes.