Even when playing open guard, whether it's spider/open seated/De La Riva/butterfly, must focus on breaking the opponent's posture. Grab the collar when playing open guard once the opponent leans in. Use the lasso to pull the opponent down. Use a spider bicep control to drive the opponent forward off their center of gravity. Get the underhook and good lat control by pulling them in. Otherwise, one must limit their movement by tight control of their legs and hips by moving in to seated guard, X-guard, half-guard, deep De La Riva, or foot on hip reverse De La Riva.
When maintaining guard on one's back or trying to use butterfly hooks or keeping a relaxed seated open guard with a forward lean, must keep the knees at a 45 degree angle from one's centerline and inside a 90 degree angle from one's torso. If a knee (and thigh) gets pinned down more open than that, it is virtually useless since one cannot push nor lift with it. If it is too closed of an angle and vertical, then it can be pushed out of the way and collapsed. If it is too far from one's torso, then one loses most of one's power.
Sweeping from open guard is largely about timing and working the action/reaction. With a good grip and control of the opponent's posture (see above ;), one can easily initiate sweeps when the opponent leans forward and commits some of their body weight. One can remove two posts or more easily lift and thereby control their hips with the right timing. This enables hitting sweeps.