Without getting too metaphysical and going way beyond my pay grade, we experience time in a number of different ways. How we relate to the present differs from how we relate to the recent or even the distant past, and all the way stations in between have their own subtle distinctions. As writers we can express these through the tenses we select.
Here are some of the ones we commonly use:

  • Present: I write
  • Present Continuous: I am writing
  • Simple Past: I wrote
  • Past Imperfect: I was writing
  • Past Perfect: I have written
  • Pluperfect: I had written
  • Conditional: I would write 
  • Conditional Perfect: I would have written
  • Future Perfect: I will have written

In these examples the present is condensed and authoritative: I write – it’s a statement of fact, whereas the present continuous I am writing sounds a little more hesitant and open-ended. The real nuances start to make themselves felt when you venture back in time. I wrote is direct and straightforward, but I was writing is somehow more suggestive: I was writing… (and then something happened to stop me?) I have written sounds emphatic, taking three words to hammer the message home. I had written takes you farther back still. It’s a dead tense, an inaccessible one and I don’t like it at all. I would write  sounds like someone hedging their bets – I would write but… but… but – it’s an uncomfortable tense, a mitigating tense, but it’s not quite so hand-wringing as the conditional perfect – I would have written (but it’s too late now.) The future perfect sounds wonderfully organised and efficient, redolent of forward planning: I will have written. It’s self assured in a way that the imperfect never can be.
Try substituting different verbs: I would have loved, I was hurting, I rejoice, and you start to see what a crucial contribution the choice of tense makes to what you are trying to convey. Choose wisely and you will have done yourself (!) a great favour.