Try and buy loose leaves rather than those that come in a bag as some bags are pumped full of ‘preserving air - no joke! When you go to the supermarket look for the bags that say: ‘stays fresher for longer’; that’s those preservatives added. (Really? What will scientists come up with next to make money for food giants!) If you buy a bag place a bit of kitchen towel in it as it helps keep the leaves fresher for longer.
Never dress a salad before you serve it, it takes 30 seconds for vinegar to start wilting the leaves. I like to leave my salads undressed. By adding herbs and seeds you can often go without a dressing, things like tomatoes, avocado, salmon etc. all add moisture to your salad. This summer I am loving dill in my salads so am chopping that in almost every one. If I do, do a dressing, especially one with vinegar, I leave it on the table and let people dress their own.