The best trick is to get the denominator of all to the same number, I am sure you were aware of this.

But this is not always the easiest thing to do. Take for instance Q1 above. Here the denominators are 7, 8, 10, 13, 35....13 & 7 being prime, each of these fractions will have to be multiplied by 13*7*2*5*2*2. This is not the easiest thing to do.
Another quick approach I always use is this.

Note that for every positive p & q, p/q is < (p+1)/(q+1).
This will easily help you solve Q1 above.

For Q2, you can reduce the terms to 3/8, 5/7, 7/8, 6/8.
It's clear that 3/8 is the lowest and if you apply my trick here, you will know that out of 5/7 , 7/8 and 6/8 - 7/8 is largest.

Hope this helps.