Text isn't necessary on a thumbnail, but adding it will give your reader more of an idea what your blog is going to be about. However, sticking with one old boring font will become more and more monotonous over time, so here is a guide to picking the right font for the right occasion.
1. Which Era is Your Blog Talking About?
If your blog is talking about Wilhelm Steinitz, Chaturanga, or something in olden times like that, don't use a modern font. Fonts such as and similar to Times New Roman work best, giving the feel that we are in olden times.
On the other hand, modern times pose a different idea. A blog about AI in chess might have a robotic, sort of square font. A blog about a certain type of opening might have a theme like that - for example, you might use a fancy cursive font in the thumbnail when talking about the French Defence.
BUT IT NEEDS TO BE EASILY READABLE. DON'T USE FONTS LIKE THIS ONE:
2. What Colour is your Font?
The colour of your font is really important. As with the previous section, it also needs to be related. A thumbnail about AI in chess might have an electric sort of blue text, while in olden times you might just give black text. If it's about a player, tournament or related that nobody knows about, you might include fading text.
No matter what colour you choose, the text also needs to be readable. Don't make it too close in colour to the background. If you want to keep the same colour, you can just add an outline too, like in this thumbnail of mine:
3. Where The Text Is
One of the most important things is the position of the text. Usually, text isn't the main part of the thumbnail (with images and stuff instead) so you want to move it to the side. Try not to make it clash with the images or important parts of the thumbnail. Overlapping the images is fine when you want your reader to see the text, or you want it to pop, but don't completely block things. Let them still be seen; you can overlap a little bit, but don't overlap the whole image.
4. Size
The size of the text is one of the most important factors when inserting text. I like making it big enough to actually be able to read, but small enough to not take away all the attention from the rest of the thumbnail. If it is not the centrepiece of your thumbnail, or if it is not very very important, don't make it too big. Subheadings should be even smaller if you have one - maybe right underneath your big text and in a smaller size, so that only when readers click into the blog can they see it. This is one of the most effective ways to clickbait.
So, in final for this section, not too big and not too small, unless you have a special reason for doing so. Usually, making text the centerpiece is less effective than having a cool image, as images actually visualise things and just look cooler in a way. Text - you actually have to read it and it just isn't the same. You can't visualise it as easily.
5. Effects
If you make your thumbnails on a website or app that specialises in them, you might be able to find that you can make what is called an "effect". These make the text more interesting to read on the thumbnail, and can easily catch a reader's attention. You can have this:
Or this:
Or this:
And much much more. Cool effects on your text just make it pop, causing your thumbnail to be even more clickbaity. Looking brighter also makes it more clear to see your text, which is another win-win! Overall, cool effects on your text just make the boring old text look better in whatever way you have chosen. Play around with effects and you might soon find one you like!
6. Don't overdo it
This is probably the worst mistake someone could make: overdoing it. Too much text on the thumbnail will make nobody want to read it, as there is too much. It is overwhelming and there is not much space left for the images themselves. Make sure that you do not add that much text: three textboxes maximum, I would say. Having no text at all is better than too much text.
Also, make sure that in each textbox, there should only be one or two lines of text. Too much text will take too long to read, and nobody wants to do that. This also means you need to squash it in, making the text smaller, which as we said was bad.
So bottom line: don't add so much text and you should be okay.
Conclusion
Welp, you survived! I hope you have learned a few things and will now improve your thumbnails! If you find any of the hundreds of things that I missed, please help me with more of these ideas, I would love to add on and help everyone make better thumbnails!