print number criticism in Nasm - numbers

Question

I have written a "method" is Nasm 64bit mode. I just want some advise on how I could have done it better as I have just started coding in Nasm. For example is there a way to use less registers, or are my naming conventions horrible(they probably are!), is there a better way to print negative values, etc.
bits 64
section .text
global _start
_start:
;debugging
mov rbp, rsp
push -666 ;number I want to print
call _printVal ;calling the print "method"
;exit
mov rax, 1
mov rbx, 0
int 80h
_printVal:
;prolog
push rbp
mov rbp, rsp
;save registers
push rbx
push rdi
push rsi
;actual code
mov rax, [rbp + 16];get value user wants to print
mov rbx, 10 ;we will be dividing by the to get the last digit
xor rcx, rcx ; clear the rcx register as this will be out counter
cqo; extend the flag
cmp rdx, -1 ;check to see if negative
jne _divisionLoop;if not negative jump
;print negative sign
push 45;negative sign value
mov rax, 1; sys_write
mov rdi, 1; stdout
mov rsi, rsp ; address to what to print
mov rdx, 1 ; how many bytes is it
syscall
pop rax ;pop negative sign value from stack
mov rax, [rbp + 16]; get user value again
converting negative value to positive
dec rax
not rax
xor rcx, rcx; clear rcx because of syscall again
_divisionLoop:
xor rdx, rdx
div rbx ;divides number by 10 to move over last digit into rdx reg
push rdx ;pushes the remainder onto the stack
inc rcx ; count for how many digits added to stack
cmp rax, 0
jnz _divisionLoop ;jump if the division did not result in a zero
mov rax, 1; sys_write
mov rdi, 1; stdout
mov rdx, 1; 1 byte long
_printToScreenVal:
mov rsi, rsp; pop value from stack (most significant digit)
push rcx; (save rcx)
mov rcx, 48
add [rsi], rcx; add 48 to make it into ASCII value
syscall
pop rcx; get rcx register back
pop rbx; pop most siginificant digit
dec rcx; decrement how many more digits i have to print
jnz _printToScreenVal
;restore register
pop rsi
pop rdi
pop rbx
;epilog
pop rbp
ret