I'm rapidly realizing that it's kind of hard to think of kitchen tips! I probably do a lot of things that others would consider tips, but they're either like second nature to me so I don't think about it, or else I've picked them up from someone else so they're not original and I feel weird about posting them. But I'll keep thinking...
Here's one thing I do from time to time that sometimes helps speed things up in the kitchen. I started doing this a couple of summers ago when my onions were ready to be picked from the garden, and I wasn't going to use them all up before they started going downhill (I grow walla wallas - they don't keep in the ground as well as some others).
I took a bunch of onions and peeled them all, then chopped them into the standard size I use in all my cooking (I put onions and garlic in just about all of our entrees, even if the recipes don't call for them). Then, I took some old ice cube trays and put the onions evenly into them, added a tablespoon of water to each cube section, and froze them. Popped them out of the trays and into a freezer bag. Then, when I need onions for whatever I'm cooking, I just have to grab them out of the bag, throw them in the pan, and it's ready to go. No muss, no fuss. No chopping, and no crying! I use about four cubes for one medium onion.
I've also done this successfully with celery. One of these days I'll try it with bell peppers. I have heard it works well with certain herbs, like basil and parsley, but I haven't had enough of a crop to try them yet. I need to try it with cilantro, which always grows much faster than the rest of our salsa ingredients!