There are plenty of tricks and techniques.
The first is good posture and stance. Stand with your feet at least shoulder width apart and keep your elbows tight to your body.
Many people turn the camera left when shooting in portrait mode, thus causing their elbow to be sticking out. If you turn right and bend your wrist, you can keep your elbow into your body.
If you can, lean against something solid...a post, a tree etc. Maybe sit or kneel so that you are using something for support. If the light is really low, you might even need to hold the camera against something solid.
Breathing techniques also come into play. Just like when shooting a gun or other type of projectile weapon, you want to steady your breathing and fire the camera during a pause.
If you can't/don't use a tripod...what about a monopod? One trick is to tie a string/rope/belt to an eyelet and screw that into the tripod threads...then put a loop in the bottom and use your foot to hold the string to the ground. Then when you pull up with the camera, it is steady...at least for vertical movement.
Of course, you could use a lens that has IS. The 24-105mm F4 L IS comparable to your 24-70mm. A stop slower but IS will really help combat shake.
Also, your 24-70mm is one of the heaviest lenses...some people find that weight makes it easier to steady...and some find it too heavy.