When positioned on the ground pulling weeds, the head tends to be down, with the upper back rounding over and shoulders pulling forward. Too long in this position will cause an aching pain in the neck and back, so before that happens, every 5 -10 minutes or so, counter-stretch that position by opening the chest and pulling the shoulder blades closer together, while looking upward. This takes the spine from a rounded position, to an extended position.
When raking or using a hoeing, try to position your body so that one leg is lunged slightly forward with a bend in the knee, so that you may easier maintain a straight spine. And at least every 5 or 10 minutes, take a good counter stretch. I like to use the rake handle to assist, by holding the rake in a horizontal position in front of my body, with my hands a little wider than shoulder width apart. Then I raise the rake over-head and back, reaching as far enough to feel a good stretch in my chest and shoulders. You can also get a great stretch for the entire side of your body if you hold the rake straight up above the head, then lean to one side for a few breaths, and then the other side.
When you are reaching overhead and looking up to trim trees or bushes for any length of time, counter that reach with a standing forward bend, just letting the head and arms dangle toward the ground so your back and neck can relax. The hands and wrists always need some TLC, so take time to spread the fingers and turn the wrists. Interlace the fingers and press out through the palms to stretch the forearms, wrists, and hands. Gently press the fingers of one hand against the other palm and do this with the thumbs as well to stretch each finger individually.
The biggest lesson I"ve learned in almost 15 years of gardening regularly, and admittedly I"m still trying to learn, is to not take on everything at once. I"ll go out one day, and commit to just one area of the yard, and finish before I am anywhere near exhausted. That way I will be feeling good enough to move on to the next part the following day. As every gardener knows, the work is never completely done, at least not until fall rains arrive! So, take your time and pace yourself, we have a long season of sun approaching."