It's been a while since I've added a tip so here goes.
I spotted a feature on a Giottos tripod the other day that reminded me of a useful stability tip you could try.
One way to make your tripod much more stable is to weigh it down. Doing so will make it seem like a more expensive heavy duty model. The easiest way is to carry a plastic shopping bag (or better still one of the new recyclable canvas ones). When you get to your location look around for some heavy objects - bricks or stones are good. Slip one of the bag's carry handles over the centre column so it's resting on the collar, just below where the three legs meet. Fill the bag with the stones and pull the other carry handle over to stop it dangling to one side. This heavy weight will pull the tripod down making it rigid and super firm.
Another option is to use your camera holdall as the weight. If you arrange it well you can also have waist-height access to your compartments when reaching for filters etc.
The reason the Giottos reminded me of this tip is that there's a hook built in to the base of the centre column.