"Don't be a slob", "Don't accumulate shit", and "Don't be stupid with your space" are just so obnoxiously obvious as to be entirely unhelpful suggestions for anyone with half a brain cell.
And "Don't bother putting things away" is a clear sign to me that this person doesn't know what small is, because when you live in an actually small space, putting things away neatly improves your mental state significantly. You will notice your improved condition when you have that extra few feet of floor, desk, and shelf space.
Real functional advice would be things like "You'd be surprised at how much space you can save by replacing certain bulky items with compact travel/camping equivalents." Get rid of big fluffy bath towels that take forever to dry, and get small linen ones instead ( We have a few of these, and now I'd never buy anything else regardless of available space https://www.amazon.com/dp/B00WBC17N4/ ). The same goes for comforters and winter coats that you're going to want to stow in the summer, bags, dishes, and so forth.