Consistency is key when speed training. To ensure your reps are done at even pace it can be useful to look at Pace Tables so you have an idea of your 400m, 600m, 800m rep times when you are running on the track:
PACE TABLES: http://www.capitalarearunners.com/training/interval.html
This web page gives a table showing equivalent race times and then below the target interval paces you would run during a track session to train for the race time above. For example if your recent 10k time was 44:43 mins, you would look at the column that has this time in then look at the column directly below to see your 400m interval pace, which is 01:37.
A website called Macmillan Running has a ‘Running Calculator’ that is excellent for looking up your equivalent race times to give more exact numbers: http://www.mcmillanrunning.com.