"A very common problem for inexperienced players is to curve the fingers too much so that the fingertips come straight down on the hole.... The cause of this in the right had especially is putting the right hand thumb too far under the thumb rest."
Another cause is holding the clarinet too close to the body.
"When reaching for a key with the little fingers of either hand, such as playing a 3rd line B natural, be careful that the "reaching" or "stretching" with the little finger does not cause one of the other fingers to slide off of its centred position over the holes."
I think it is a good idea to play mid-staff B, and DELIBERATELY make squeaks with the first three fingers of the right hand. Try all fingers separately. Tilt each finger a little: to the right, to the left, up the instrument, down the instrument. Also try allowing a finger to just touch the 'banana'.
The do the same with the D a few notes higher (or even higher notes) but making leaks with the left hand fingers. Try rolling your left index finer slightly towards the throat A key, as if you are just about to play that A.
By doing this you get to know the high degree of accuracy needed in placing your fingers on tone holes so that you don't get leaks... how very easy it is to make squeeks. A finger must press with equal PRESSURE, right around the edge of edge of the tone hole, not just TOUCH the edge.
Eventually your fingers feel for this accurate alignment, adjusting as necessary, even when playing a slightly different clarinet, without you even thinking about it.