Always cautiously and slow and steady. This is the best approach if you want to sustainably send.
Start with 25 day 1. Then 50 day 2, 75 day 3, 100 - 150 day 4, etc. Stage it this way so you reach your desired sending volume within 2-3 weeks. Then you can maintain sending at this rate for as long as necessary.
However, content refreshes are vital. Always check to make sure your emails inbox prior to sending. You can test this here: gmass.co/inbox.