How do you avoid writer’s block?

You’ve come to the right person! I’ve been writing since I was in high school (which is more years than I want to contemplate) including weekly and monthly columns in newspapers and magazines for years and years and twenty published books (really, check out Amazon.com!)
My opinion is:
There’s no such thing as writer’s block.
What you need to do is train yourself to just write.
There are great ways to do this. I learned back in my undergraduate days by reading the influential book Writing Without Teachers by Peter Elbow. In it he posits the very simple idea that writers write and sure enough, our discipline in the writing program was to write two pages of content, any content, every single day. Don’t have anything to write? Write about not having anything to write.
The more you teach yourself that it’s a task just like riding a bicycle or mowing the lawn, the more you’ll come to realize that for almost all writing you can just sit in front of your computer and start letting the words flow.
A key idea is to let go of editing in your head as you go along too. Just let the words quite literally flow onto the page. If you can’t think of a word, do something like [what’s the fancy word that means thing don’t match up?] and keep going.
I’ve further refined this process and learned two more tricks: write with the underlying assumption that you might delete the entire sentence, paragraph or even idea later as part of your process of refinement, and if you’re really frozen, skip the first paragraph and come back to it later.
As an example of the former, if you really do learn how to just pour words onto a page in a reasonably coherent fashion, you’ll find that as you refine your argument that some of the first few ideas, points or facts you wanted to cite prove not to be particularly relevant and are supplanted by better, tighter, more effective replacements. Go with that flow, axe the earlier, weaker paragraphs and stick with the better, stronger prose.
In the latter case, many people get hung up with how to introduce a topic. What is that brilliant opening line that will just hook your readers? Skip it for now. Seriously. While the final prose will be read in a linear fashion, that doesn’t mean it has to be written that way.
Finally, if you are stuck, one more bit of advice: go do something completely different. Have a shower, go for a walk, play a game of tennis, have an ice cream cone. Push the entire issue out of your mind and let your subconscious chew on it for a while. You’d be amazed at how often you can return refreshed and ready to let it rip!
So don’t be too concerned about writer’s block. Be more concerned about learning how to see writing as a pleasure, not an obstacle.
And good luck!