Learn how to convert to binary with the most emphasis, then convert freely from binary to either octal or hexadecimal by grouping,
ie. 493 == 111101101 (base 2)
111 101 101 == 755 (base 8)
1 1110 1101 == 1ED (base 16)
This is how I did every conversion when I did 2/3U CS in the 97 HSC.