Attacking with Dimir Spybug and Nightveil Sprite
Your Dimir Spybug will get pumped in time to be stronger during the same combat.

The combat phase is divided into several steps.


Beginning of combat
Declare attackers
Declare blockers
Combat damage
End of combat


Nightveil Sprite will trigger when it is declared as an attacker, during step 2. This is when you will surveil, and that will trigger Dimir Spybug. So by the time blockers are being declared, Dimir Spybug will already have the +1/+1 counter.


  
  Declare Attackers Step
  
  
  
    508.1. First, the active player declares attackers.[...]
    
    
      [...]
      
      508.1m Any abilities that trigger on attackers being declared trigger.
    
    
    508.2. Second, the active player gets priority. (See rule 116, “Timing and Priority.”)
    
    
      508.2a Abilities that trigger on a creature attacking trigger only at the point the creature is declared as an attacker. They will not trigger if a creature attacks and then that creature’s characteristics change to match the ability’s trigger condition.
      Example: A permanent has the ability “Whenever a green creature attacks, destroy that creature at end of combat.” If a blue creature attacks and is later turned green, the ability will not trigger.
      
      508.2b Any abilities that triggered on attackers being declared or that triggered during the process described in rules 508.1 are put onto the stack before the active player gets priority; the order in which they triggered doesn’t matter. (See rule 603, “Handling Triggered Abilities.”)
    
  


Step-by-step of what happens:


Nightveil Sprite's ability triggers as it is declared as an attacker.
Before you get priority in "Declare attackers" step, that trigger is put on the stack.
Assuming no responses, the ability resolves; you surveil.
Dimir Spybug's ability triggers, and is put on the stack.
Assuming no responses, the ability resolves; Dimir Spybug gets a +1/+1 counter.
Blockers are declared.
Combat damage is dealt. Dimir Spybug has the +1/+1 counter by this time, so it will deal an extra damage (and have an extra toughness).