When the auction goes 1NT-3NT by the opponents, there isn't much imagination required. Choose your longest and strongest suit and usually lead the 4th-highest card in it. A few "what-ifs" 1) What if it is just about a "tie" for longest and strongest? With two 4-card suits or two 5-card suits, roughly of equivalent strength, prefer a major when in doubt. (Your opponents would usually look for or show a major if they had one). 2) What if you have a "sequence?" If 3 in a row (QJ10 or KQJ), lead top. If "almost" 3 in a row (such a KQ10 or QJ9), also lead top. Otherwise, tend to lead 4th best.
You might also consider getting Larry's book on Defense HERE or try Larry's Defense Webinar series which you can find HERE.
QJ52 
K76 
876 
543
As West, what is your opening lead?
South West North East 1NT Pass 3NT Pass Pass Pass Choose One:1. -Q2. -23. -84. -5Answer: 2Against notrump, lead 4th from your longest and strongest. Lead the honor only with 3 in a row or "almost" 3 in a row. With a suit headed by QJ9, you can lead the Q. (Against a suit contract, it is okay to lead the Q from QJ empty).
Your result so far:- 85 Q8742 K9763 A
As West, what is your opening lead?
South West North East 2NT Pass 3NT Pass Pass Pass Choose One:1. -82. -43. -64. -AAnswer: 24. You should opt for the major, not the minor (even though the diamonds are better). Dummy could easily have diamond length. Dummy won't have heart length (no Stayman, no transfer).Your result so far: - KJ62 A7653 J76 Q
As West, what is your opening lead?
South West North East 2NT Pass 3NT Pass Pass Pass Choose One:1. -22. -53. -J4. -6Answer: 25. Lead 4th from your longest and strongest. It is okay to lead away from an ace against notrump. Just don't do it (nor lay down an ace) against a suit contract!Your result so far: - J10873 43 AK43 62
As West, what is your opening lead?
South West North East 1NT Pass 3NT Pass Pass Pass Choose One:1. -J2. -73. -44. -AAnswer: 1J. Prefer the major. Lead top from 3 in a row or "almost" 3 in a row as here. Against a suit contract, you would probably lead the A.Your result so far: 
KQJ10 
1098 
A5432 
2
As West, what is your opening lead?
South West North East 1NT Pass 3NT Pass Pass Pass Choose One:1. -K2. -103. -104. -3Answer: 1K. Yes, your diamonds are longer, but this sequence is too much to pass up (and, you won't be hitting dummy's suit--whereas dummy could have 4 or even 5 diamonds).Your result so far:- J542 82 10987 862
As West, what is your opening lead after this much more involved auction?West North East South 1NT Pass 2 Pass 2 Pass 2NT Pass 3NT Pass Pass Double Pass Pass Pass Choose One:1. -2
2. -83. -104. -Your system's
leadAnswer: 28. Partner's double is for penalties. It also says "please lead dummy's suit". From a doubleton, you lead the higher one. North used Stayman in an attempt to find a fit for a four-card major. Since they didn't raise spades, that must mean North's major is hearts. Without the double, we'd lead the 10.Your result so far: - J82 J5 J832 J832
You are West, What is your lead?
West North East South 1NT Pass 2 Pass 2 Pass 3NT All Pass Choose One:1. -22. -J3. -24. -2Answer: 32. It may seem like a tossup between clubs and diamonds, but you have a bit of extra information from the auction. Partner could have made a lead-directing double of clubs. It's not much to go on, but it's enough to tilt the scales in favor of a diamond lead. If you would like to learn more about Opening Leads, you'll find it in Larry's book.
Your result so far: