There are a few things I like to focus on. There are books written about your question.
If it gets cool, try not to sleep in the bottom near water, it will really be cool down low. Even a couple hundred feet up on a bench from the bottom of the draw will stay more dry and warmer at night. You may be OK in Sept in CO.
Make sure someone you know well knows where you will be and when you will be out to make a phone call. Solo is not dangerous, but if you get dinged or hurt solo, it can turn that way. A satellite phone is handy. I hunt solo a ton and have not had any problems, I just take extra care in how I hunt ie, what I will climb up and down in the way of cliffs, etc.
I'm sure you have read everything under the sun in the way of elk hunting with a bow. # 1 is always consider the wind, elk can smell us 1/2 mile or more away and have no tolerance for us. Be patient, don't call too much when trying to locate elk. Call during the night and spike camp near the bugles so you can be there in the morning at first light to stalk into them. If you find an active wallow, and it is a hot day, sit that wallow from 2 pm until dark on the downwind side. When you do call elk, always knock an arrow and make sure you can move your feet without making a bunch of noise, clear the ground under you. Some elk will just come in silent or they may run in - I learned this the hard way.
Take a range finder, elk will look huge to you compared to deer and it will be harder to judge distances. On the shot, don't try to snug the shot into the shoulder pocket. Elk have huge lungs and there is a dinner plate kill zone behind the shoulder, mid body vertical. There is no need to flirt with the armor plated shoulder blade of an elk.
Make sure you drink a ton, and use something like Wilderness Athlete to replenish your fluids. Be sure to journal your hunt some way, so you can remember it in a few years and so we can all read it when you get back. It is a blessing to be among elk in the mountains. Best of luck and be safe.