Comment by higherhalf

This can be done even simpler:

  global _start
  _start:
      jmp next
  string:
      db `Hello World!\n`
  len: equ $ - string
  next:
      mov ecx, string
      mov edx, len
      mov ebx, 1
      mov eax, 4
      int 80h
  
      mov ebx, 0
      mov eax, 1
      int 80h

For NASM, it can also be put into a macro, for example printing to video memory at 0xb8000:

  %macro print 1
      mov ecx, %%loop_start - %%strdata
      mov eax, 0x0700
      jmp %%loop_start
  %%strdata: db %1
  %%loop_start:
      mov al, [%%strdata + ecx - 1]
      mov [0xb8000 + ecx * 2 - 2], ax
      loop %%loop_start
  %endmacro