This is a voluminous topic, for which this is just a quick summary.

Points for Honors

It is well known that Aces and Kings (A=4 and K=3) are undervalued by the 4-3-2-1 count.  Also, Queens and Jacks (Q=2 J=1) are  overvalued.  Probably 6=4=2=1 would be more accurate, but nobody wants to overhaul things that much. 

Some teachers like adding 1/2's and subtracting 1/4's.  Too complicated.  I like this simple approach: "When your hand is prime (mostly aces/king), take the higher road. When you are very queeny/jacky, take the lower road." In other words, upgrade a bit when you have aces/kings and be pessimistic when you are full of mostly queens and jacks.

Spot Cards

 What about 10's and 9's?  When stray (such as 10xx or 9xxx), I don't pay much attention. But, when they are in conjunction with higher honors, such as A109x or J109x, then I upgrade.  I "bid one more" when in doubt.

Short Suits/Long Suits

The age-old question: Do I count for these and how? The quick answer is: Not too much until after you've heard some bidding. When you first pick up your hand and have to decide if you should open, the Rule of 20 is a decent enough guideline. Add your HCP and 2 longest suits and if that is 20, open the bidding. I recommend opening most 12 counts (if 4-3-3-3 and vulnerable and it is junky/queeny/jacky then I can live with a pass).

Long suits are definitely worthwhile in notrump contracts. Add for a decent 5-card or longer suit (rule of thumb is to add 1 for each card starting with the fifth card). If opening 1NT, add for a decent (not Jxxxx) 5-card suit. If responding to 1NT, do the same. However, if partner opens 1, for example, and you have:

Q32
2
J32
AQ6543,

I wouldn't go crazy adding points for those long clubs. Those extra clubs will often be completely useless, especially if partner is short in clubs.
Long suits that get raised are surely worth extra. If you open 1 holding KJ876 and get raised to 2, life is good. Picture partner with Qxx. Now, your side is likely to take 4 spade tricks. Contrast that with if partner responded 1NT, maybe with x. Now, you are nowhere near 4 spade tricks. So, clearly add points for long suits that get raised.

Short suits are nice, but really worthwhile when supporting partner. If you are dealt, say Qxx and a singleton heart and partner opens the bidding 1, your singleton is actually a negative. Not good at all. But, if partner opens 1, then your singleton heart is great. Add 2 points for a singleton, and 1 for a doubleton (and 3 for a void). If you have more than 3-card trump support, add even more. Exact numbers aren't important, but a decent guideline for counting shortness when supporting partner is as follows: "Subtract your shortness from your trump support and count accordingly."  Example: 3-card support and a singleton is 3-1=2 points (what you are already used to).  4-card support and a singleton is 4-1 = 3 points.  5-card support and a void is 5-0=5 points. 

I Feel Good

This is one of my favorite teaching examples:

4
KJ654
32
A8765.

Should you add for the 5-card suits? Should you count the singleton and doubleton?  Answer: Not yet.  Listen to some bidding first. Partner opens 1. You respond 1NT and partner's rebid is 2.  How are you feeling? Ugh.  Your long suits and short suits all seem worthless. You pick up the same hand the next day and again partner opens 1. You respond 1NT, but this time, partner's rebid is 2!   Do you know the iconic James Brown song, "I Feel Good?"  Don't you?  Now, your 5-card heart suit is golden. Your short suits are ruffing values. You'd raise all the way to a heart game. You Feel Good!

There is much more to this topic (I hope some of you readers will join me for live lessons--one of my favorites is on hand evaluation). 

You can also see my former partner, David, discuss hand evaluation on Bridge with the Berkowitzes. 

Or you might enjoy these webinars on the subject.

 updated: August 2020