Lean not unto thine own understanding is often heard as a warning against thinking, which it is not. Proverbs is a book that praises understanding on nearly every page. The word is lean — the difference between using your mind and resting your full weight on it.
Your understanding is a good tool and a poor foundation. It works with the information you have, which is always partial, and it is shaped by what you want to be true, which you cannot fully audit. Leaning on it means treating your current read of a situation as the last word, and then being genuinely shaken when the situation turns out to be larger than your read.
In all thy ways acknowledge him is the practical instruction. Not in the religious ways — in all of them. The job, the money, the way you spend a free evening, the conversation you are rehearsing. Acknowledging him is not a ritual added to a decision; it is admitting, in the middle of it, that he has a claim on this part too.
The promise, he shall direct thy paths, is not a guarantee of a route map in advance. The Hebrew carries the sense of making straight or smoothing. You will still walk it a step at a time. But the path will be his doing rather than the product of your best guess, and that is a considerably better thing to be standing on.