If you use 'in my humble opinion', you have to do it in a sentence that contains an opinion, of course. Please avoid ... is a command, not an opinion.
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CalifJimIf you use 'in my humble opinion', you have to do it in a sentence that contains an opinion, of course.
Please avoid ... is a command, not an opinion. So IMHO won't work at all there. You need to change the sentence if you really want to use that expression.
In my (humble) opinion, you should avoid it at all costs.
(Note the plural costs,
CalifJimThe inclusion of the word 'humble' shows a lack of seriousness, in my opinion.