Some tips:

Don't write everything down. Taking long notes will reduce your speed and make it harder to navigate between various stuff you've got written down.

Use mental math a lot. For instance, how much is 32*11? This would normally take a lot of time to calculate, but not if you notice a few things:

32*11 = (30 + 2)*11 = 30*11 + 2*11 = 3*11*10 + 22 = 330 + 22 = 352. Took me about 5 seconds to calculate.

Another example: is 152 divisible by 11? You should already know all the squares up to 15 by now, so you'll know that 121 = 11^2. Then start adding multiples of 11 until you hit something close to 152. I started adding 22: 121 + 22 = 143. This is 9 units away from 152, so you can safely say that 152 is not divisible by 11. Again, 5 seconds.

Memorize important data: squares up to 15 (at least), some cubes (up to 5 maybe), other important powers of 2 and 3 (for instance, it's really important to know that 2^10 = 1024).