Basics shin block
The biggest problem I see here is people lifting their legs up too high, unless it is a body kick, the foot only rises off the ground 5-6 inches. (if it is a body kick, bring the leg right up and seal the gap in between by touching knee to elbow)
When lifting the leg up, turn it out to about 45 degrees, if you just lift it up straight then you still get the kick on the thigh, just at a different angle!
Keep your leg at 90 degrees to the floor, with your foot parallel to the floor (this will keep you leg strong and stop kicks just blasting through your block)
Aim to block the kick with your shin just below the knee.
If you can get the angle of the block right, you shold be able to block against their foot...which is a real added bonus as it hurts.
remember to keep yopur guard up, as the kick could be a feint for a right hand!
Other blocks include - the cross shin block, the stomp block and a nifty little foot block that is as hard as SFUK to get right!!!
hope this helps?