In Common errors^x, Past perfect^x

Hi, Hey. Can you please tell me how should I know which form to use. Here is an example Once I (spend)__ the whole day in the jungle.I always want to use "had spent", because I'm given the time in the sentece. But the right answer should be "spent"...Why? I do not get...

Hi, 1. Past Perfect Not a good idea for the paragraph we are looking at. generally, it's a common error to use Past Perfect when Simple Past is better. 2. (would+V2): I would ride... Yes, that's OK, if you want to write about 'past habits/routines'. Best wishes, Clive