I've been told to always start a training run by running uphill - it slows you down for the rest of your run

Have a look at this link:
http://www.runnersworld.co.za/calculator/training.php

It allows you to put in a distance and a goal time. Based on these values it shows you the various different paces you should be running in training.

So my 21.1km done in 1:57:01 leads to the following values:
Your easy run training pace is: 6:25/km
Your tempo run training pace is: 5:21/km
Your maximum oxygen training pace is: 4:50/km
Your speed form training pace is: 4:28/km
Your long run training pace is: 6:25-7:14/km

It includes an explanantion of each category as well.

My training pace (I consider as my easy run) is usually about 5:50/km which gives me about a 1:45 21kmwhich I dont think I'll get to in the near future