From The Play
Bullet #1 There are times when leading a 5 is the correct5 lead for example, you are holding one 5 and three 10-value cards and you must have 1 more point than you have after the cut. There are only 7 combinations in which you will not score the needed point; a second time is when you have three 5s and one 10-value card. You lead the 5 to avoid getting trapped multiple times; the third example is on the 3rd card; this is the scenario:
I am the pone (non-dealer of the hand). The play went
K (my play)
8 (dealer)
J (my play)
3 (dealer)

At this point the dealer most likely has the following cards: 4,3,2,5,8,7,6.
If I play a 10 value and hold the 5 for my last card, the dealer most likely will trap in in a run. A controlled/known 2 points in most cases is better than giving up 3 points.

Bullet #2: When holding low cards, it is better to lead the 3 or 4, this forces your opponent away from playing a 5 as it leaves open the run possibility.

Bullet #4: The 8 is a much better lead than the 7, you cannot play a 4th 8 in sequence as the count exceeds 32, but a 4th 7 can be played for a dealy 12 points.

In General
Bullet #2
If the lead is an 8 and you have a 7, but no other cards of 7 or less, do not play the 7 to make it 15 for 2; this is because you opponenet can score an easy 8 points on you, by playing the 9 for 24 and a run of three, then a 6 for a run of 4 and a go.

Just my not so humble opinion.

Bob Milk
Grand Master of the American Cribbage Congress (www.cribbage.org)