There are more than a few ways to ruin a perfectly good batch of muffins so I thought that I would save you the trouble. Here's a few things that I have done wrong... and in no particular order.
1. Not reading the directions correctly. You should always read them at least twice. The minute that you find yourself in a rush, you can completely miss steps.
2. Adding rancid nuts to a batter. You should get into the habit of keeping a small amount of nuts in a jar for daily use. Adding a few nuts to a salad, a tub of yogurt etc is a great way to add protein to your snacks.
3. The remaining bag of walnuts that you brought home from the supermarket should go straight into the freezer. They will remain fresh a lot longer in the freezer than in the cupboard. I have one more point when it comes to nuts that you might want to add to the batter. Carefully check for bits of the shell that has made its way into the bag. The last thing you want is for your guests to break a tooth on a bit of shell.
4. Before preparing the batter, bring all of the ingredients and place them on your work area. It might be a good idea to double check that you picked up the baking powder instead of the baking soda unless that's what you need. I for one, buy all of my baking soda and my baking powder at a bulk food style of store. When I get the ingredients home, I transfer them to a jar with a wide opening. While this has worked out quite nicely, I have often reached for the wrong jar by accident. Be sure to double check your ingredients before adding them to the batter.
5. If you don't already have a sifter, you might want to invest in one. Muffin ingredients needs to be gently incorporated into the batter and lumps can easily left behind. Using a sifter, prevents this from happening.
6. If you like the outside of your muffin with a bit of a crunch, leave them sitting on the rack for no more than a day. If you leave them longer than that, they are almost inedible. At the end of the day, transfer them to a cake preserver. The crunch will be gone, but you will be able to keep them a little longer.