First of all you need to clearly understand Intel 8086 Microprocessor architecture, different segments registers(CS,DS,SS and ES), different pointer and index registers (like- IP,BP,SP,SI,DI) and about 8/16-bit registers(like, 16-bit registers:AX,BX,CX,DX and 8-bit registers: Ah,AL,BH,BL,CH,Cl,DH,DL) used in 8086 microprocessor
Secondly, you need to understand about different instructions sets used in 8086 and then about different assembler directives and the interrupt functions (like int 21h, int 10h,etc) and the related function numbers (like, mov ah,02h , here 02h loaded in ah register) and about DOS/BIOS mode.
Thirdly, you need to understand about the programming logic development and code format and then start coding and execute the programs using MASM/TASM or Emulator(emu8086).
