improve squat,bench & deadlift

I would not vary my squat stance week in week out. Dam no! I'd lift as per my comp most of the time.

Possibly worth doing a block of training with a different stance if you really think that would help but only way out from a meet. Or if you think a different stance would help do it as an assistance lift as in the bench press-close grip bench press way.

I find deadlifting the trickiest to get right in training. Me personally, I need to get my volume in on lighter loads with limited heavy work. I like to use one top set followed by a lot more lighter work. I'll cycle both types of set over 4 weeks. This will be inished of with an assistance lift dependent on weakness is in the lift. I use low pin pulls or platfrom deads as I have a good lockout but weaker in the bottom range. Or if I fancy something lighter then SLDL and power shrugs

Once you reach a base level then for me its all about training weaknesses. Deadlifting/benching/squatting will only get you so far. If you want to shift any big weight then you'll have to consider your weaknesses in each of the lifts, choose your exercises to strengthen them and tailor a program to encompasse these lifts and provide adequate recovery. 4-6 weeks cycles are a good way to do this, 12 week comp build-ups are also pretty common. Don't underestimate the importance of accessory lifts, make sure you're eating enough and rest. Simple, common sense stuff really.