Using Serpent Sting to refresh buff is a good idea, spamming it as a SV hunter frontloads a chunk of damage but I do find Arcane Shot better as a focus dump, it throws out more focus and a bit more damage too, but if SS is due for renewal, use SS instead of cobra shot.
Another trick I like is using Fervor instead of Dire Beast or Thrill of the Hunt, it's the most predictable of the three so I activate it when I've just dumped a load of focus to maximize its effect.
Hope this helps!