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Always be kind to yourself, and forgive yourself for failures. Even if you screw up badly or feel like you deserve it, not being kind to yourself only hurts you more, it doesn't ever help you, or anyone else, in any way. It's essentially camouflaged self-sabotage. Real attempts to get better don't end up with feeling worse for trying. Appreciate your success in trying to do something for yourself instead.
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Focus on noticing when you're starting to sink into intrusive or self-destructive thoughts, and on deflecting them whenever you can. Just think anything else. The opposite of what you're thinking, or generic compliments towards yourself. When you fail, and you will, refer to #1. The point is to slowly work on making your mind less likely to go down those routes, and dissociating your thoughts and actions from negative feelings and thoughts.
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Your thoughts and mind as a whole are there to help you succeed, whatever success means. The thoughts that lead to stress and other bad emotions, unless critical to reaching decisions or taking action, don't have real value and you should let them go as well.
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The same is harder to do but can be done with focus. Don't actively focus on bad shit, like emotions, feelings, situations. Doing that doesn't help you overcome it, it just makes you feel shit, and feeling shit about something makes your mind afraid of it. Bad shit will still be bad enough on its own, there's really no merit to giving it any more space in your head than it occupies on its own. This can do wonders against anxiety.
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Let yourself fail and forgive yourself for it. If something is overwhelming you, or you can't seem to manage it, just let yourself give up for the time being. Dwelling on it will only make you feel like garbage, you'll likely fail, and your mind will associate that with trying, making every subsequent attempt harder and harder. Either do it, or don't, no dwelling, ever.
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Expanding on the last one for executive dysfunction specifically: Make a point of actively deciding to do or not do something whenever you can, instead of letting your subconscious decide. Whether it's getting up to drink some water, or whether to apply for a job, bring your actions under your agency. You decide, not your subconsciousness - even if you relegate a decision for later, do it as an active choice. Every small thing counts, and doubly so if you can get to a mindframe where you value these small successes.
Given enough dedication to them, #1 will make trying to get better in any form easier, #2 & #3 will give you more mental space for thinking and decisionmaking, #4 & #5 will help with anxiety a lot, and #5 & #6 help push back against executive dysfunction.
All that said of course, if you're struggling, a mental health professional can do much more with your cooperation than you can alone working within constraints of your mind.
And from personal experience, rule #1 is critical. If you can't manage it, you shouldn't be attempting self-help, the risk of using any insight and progress you make as self-sabotage is too severe. Cycles of "I got so far but even this was hopeless in the end" is precisely why my mental health escalated from "I'm stiffled by my environment" into 8 years of near-complete dysfunction. If you can't stop working against yourself, you really shouldn't be looking for more tools that let you reach deeper inside your mind.
Anyway, I think that sums up most of my thoughts on self-help from over the years. There might be more, but I can't think of them off the top of my head at least.