You just need to find the largest power of 2 that is less than x, then subtract it from x; repeating the process until you get 1 or 0, which is the unit digit. The power numbers indicate where there is a 1 in the binary (counting from 0, right to left). Ex,
135-128 = 7; 7-4=3; 3-2=1, so the right most digit of the binary is 1.
2^2=4, 2^7 = 128, so there are two 1's in the 7th and 2nd places(counting from 0, right to left). So the final result is 10000101.
2) To convert octal to binary, or binary to octal, you just need to replace 1 octal digit with 3 binary digits as below. Add leading 0's as necessary.