Create your list of words, names or tasks. Keep the list simple with one to two words for each item. For example, if your errand is to go to the bank, your word would be "bank." If your grocery list included canned diced tomatoes, your word would be "canned tomatoes."
Form an outrageous visual image of the first item on the list. The more outrageous the image, the more likely you are to remember it. The first word is important because you will need to recall that word first without any prompting. So for a grocery list, you might think of a can of tomatoes standing in the doorway of the grocery store.
Link the first item with the second item on the list. Now that you have the first item in mind, think of the next word on your list. For example, if you also needed to buy milk, you might picture your can of tomatoes riding a black-and-white cow. If you needed to go to the bank and then the post office, you might picture a large dollar bill mailing a letter.
Continue by linking the second item with the third item on the list, and the third item to the fourth. The key is to visualize only two words at a time so that it is easy to remember both items individually.
Think of unique images for the items so you won't forget individual items. For instance, you would not want to use the image of a cow for milk and then later use it again for beef, or you might confuse the two images for just milk and forget about getting beef altogether.
Practice this visualizing technique with a longer list of words. Start with six words and increase the list as you fine-tune your skills. Remembering a list of 20 to 30 words is not impossible to do if you have a very long shopping list.