the best non-specific advice i can give is to actually think.
stop reading things on autopilot in every context. when people communicate they do it in a certain fashion, they have a message and there are aspects of the way that they speak that tell you things about them. 'english techniques' are just people shoehorning the way that people communicate into labels and making it sound a lot more advanced than it really is. in reality you learn what a metaphor and simile is in primary school so you can communicate. i've just used inclusive language, an active voice, emphasis and hyperbole when in reality ive just yapped while finishing off my morning coffee.
if you want to learn to write an essay, read an essay. not some 99 atar kid's essay who got lucky with their cookie cutter essay during the hsc, go and read critical publications from academics and take note of the structure, and how they actually argue. how do they get from point A to B? an essay is not some kind of linguistic wizardry that you just don't 'get' because the only problems you know how to answer are one dimensional 1 + 1 = 2 with a few more letters and squiggly lines. when you try to convince someone you are right in everyday conversation (assuming you have some semblance of logical processing ability), you are doing, in short form, what is no different to an essay.
stopping waffle is done by thinking about what your words are actually saying. read your sentences, and think, 'what does this add to my argument', if the answer is nothing, get rid of it. a common example is people restating their topic sentence as a 'conclusion'. that's not a conclusion and its a waste of words and the marker's short-term memory. a conclusion is what you infer or reason from observed or communicable data. it adds something to what was seen or said before.
i think a good 90% of people's problems on here in relation to english would be solved to a good extent by just actually turning their mind to the world they are living in and how people work.