The EBU Acol file suggests the following guide.
Hands with at least 12 HCP may be opened
With 9-11 HCP, use the Rule of 20. Add the number of cards in your two longest suits to your HCP. If the total is 20 or more and most of your high cards are in your long suits, open the bidding.
With borderline hands, take into account the quality of the suits, intermediate cards and whether you have a convenient rebid over any response.
This is a very good summary and mentions the four basic criteria for opening.
High card points (HCP) Distribution (Rule of 20) Suit Quality and Intermediate cards.
One other factor is Controls, Aces and Kings particularly.
To fully understand how all these come together here is a brief history of the development of hand evaluation.

Way back before 1920 the standard method of hand evaluation in the original Culbertson System was by Honour Tricks
To value your hand you added up your Honour Tricks based on
AK of the same suit =2 Honour tricks
AQ in the same suit= ½ Honour Tricks
A or KQ or KJ10 in the same suit =1 Honour trick
Kx , QJx =½ Honour trick
You then added one plus value for any Queen not already counted and any Jack in a suit with a higher honour.To open the bidding you needed
2 Honour tricks and at least 2 plus values and a six card suit
or 2½ Honour tricks and at least 2 plus values and a 5 card rebiddable suit
or 3 Honour tricks with two suits

Next came the High Card Points System said to have been invented by someone called McCampbell around 1915 and publicised by Milton Work and known as the Milton Work Point Count for a long time.
Originally intended to value a hand only for No Trumps it was taken up by Culbertsons great rival Charles Goren and modified to include points for Distribution.. Culbertson rubbished it but it has stood the test of time.
As you will have been taught you count 4 HCP for an Ace 3 for a King, 2 for a Queen and 1 for a Jack
The basic principle is that there are 40 points in a pack and therefore the average is 10 per hand; If you have more than the average you are on your way to opening the bidding.
For No Trump valuation you only add your high card points.
In suit contracts you then add 1 point for a Doubleton, 2 for a Singleton and 3 for a Void.
An alternate way of doing this, particularly in the USA, is to add Length points. This means that you simply add 1 point for each 5 card suit, 2 for any 6 card suit and 3 points if you have a 7 card suit.
Thus with 10 High card points and two 5 card suits by the first method you would say 10 HC points and 3 distribution points (either one doubleton and one singleton or one void) totaling 13 and by the second 10 plus 2 points for two 5 card suits making 12 in all. Both quite close together.
Then in the 1990s the earlier system came back into vogue, some simply adopting the old system but Ron Klinger the Australian expert suggested adding 5 points for a void and 3 for a doubleton. And then add 1 more if you hold all 4 Aces and deduct 1 if you don’t hold any.
Goren recommended that using this method you opened any hand with 14 or more Total points but with 11-13 you added Quick Tricks which were based on the main elements of Honour tricks. AK of the same suit =2 QT, AQ in the same suit= 1½or A or KQ the same suit =1 QT and Kx =½ QT.
With 11 to 13 you could open with 2 QT or better.see Rule of 20 below.

Another useful system of valuation is the Losing Trick Count. Many players think this a relatively modern invention but in fact it was invented in 1935 by the American F. Dudley Courtenay and the Englishman George Gordon Joseph Walshe. The method was popularised in this country by Maurice Harrison-Gray one of the great English players from the mid 1930’s until his death in 1968
It is a method used in determining the level to bid when you have a known fit in a suit
Briefly it looks at the top three cards in a suit, or less if shorter, and counts as follows :
a void = 0 losing tricks.
A singleton other than an A = 1 losing trick.
Any two card suit is 2 losers unless one is an Ace or King (AK stiff would be no losers)
Any three card suit or longer is 3 losing tricks less any Ace King or Queen held in that suit.
Finally you add 1 loser if the hand is Aceless.
For this to work the Responder has to assume that if their partner opens they have a 7 loser or better.
For more detail go to Losing Trick Count.

Finally the most modern introduction to this area is The Rule of 19 (or 20)
This is simply adding up your HC points and the length of your two longest suits and if comes to 19 or 20 depending on which you are using then you have an opening bid.
Ron Klinger proposes that you add your quick tricks and make 22 the opening criteria.
So there are a number of different methods of deciding whether a hand is worth opening which are surprisingly close together.
You can test various deals to see how each method applies but using this example hand

♠ Axxxxx, ♥ AKxx, ♦ xx, ♣ xx

Culbertsons Honour Tricks System 3 Honour Tricks, two suits and no plus values but fits the criteria for an opening bid
Goren. 11 HC points plus 2 for doubletons only 13 but 3 Quick Tricks so still okay.
Length points System, 11 HC points and 1 for a 5 card suit =12 making it border line but rich in Controls so you would open.
Rule of 19 11 HC points and 9 suit points=20 and 3 Quick Tricks so also fits Rule of 22
Losing Trick Count As you open 1 Spade can Partner expect a 7 loser hand to decide on his raise in Spades if they have a fit.
Spades 2 losers, Hearts 1 loser, and 2 losers each in the Minors add up to 7 so yes they can.
It is obvious that which ever system you use provided you allow for Distribution and Controls in some way you should always know when to open, when not to bid.

The other two factors mentioned at the beginning were suit quality and intermediates

Two examples
Opening one of a suit ♠ 43, ♥ KQJ987, ♦ A62, ♣ 54 (10 HCP, 12 with Distribution, 12 with Length, fits Rule of 19 and has 2 Quick Tricks,but the quality of the suit outweighs this slight minus,is a 7 loser and it fits all the criteria)
♠ Q6, ♥ Q86543, ♦ A76, ♣ K5 (11 HCP, 13 with Distribution, 13 with Length, fits Rule of 20, is a 7 loser, has only 1 Quick Trick and a poor suit)
Certainly in first or second seat you shouldn’t open but once your partner is a passed hand you can relax the criteria if you feel there may be advantages in opening. A good suit to direct Partners lead in defence or Partner may support and either pave the way for a good sacrifice or pre-emp the opposition out of their best contract.

Interestingly if you are playing weak two openings (normally 6-10 HCP and a six card suit) opening 1 ♥ with the first is a better description of the hand and opening 2H with the second describes the hand perfectly

Opening 1 No Trump (HCP, Suit Quality, Controls and Intermediates all come into play but not distribution)
♠ QJ109 ♥ QJ109, ♦ K987, ♣ Q109 only 11 HC points but marvelous intermediates, the Hearts and Spades are almost certain to generate two tricks each.
Always remember when considering opening 1NT QJ10 is a guaranteed stop just as an Ace is so can be upgraded to 4 points in borderline hands
♠ AK54 ♥ 9673, ♦ KJ2, ♣ J8 which is 12 HC points but a much poorer hand than the first.

Use things like this to sway you in one direction or the other when your decision to open is borderline.