To work in assembler, you need to have a thorough knowledge of the CPU's programming model (i.e. what all the registers, flags etc are for) and a thorough knowledge of the op codes and their effect on the registers, flags etc. Don't use an op code unless you understand exactly what it does; wishful thinking is a common source of bugs.
You also need to be able to step through the code and work out where it's going wrong. If, like me, you started out by hand-assembling assembler mnemonics into hexadecimal machine code on paper, you do this with pencil and paper or in your head. But nowadays I suppose debuggers are the way to go. Presumably the assembler you're using has an accompanying debugger and disassembler for the CPU you're using? If not, you need to find one that does. Sorry, I don't know x86 assembler so I can't offer any specific help. In my day the targets were 8-bit microprocessors and a 1MHz clock was considered fast. ;-) David
