Once you have noticed set patterns of betting, it means that you have reached a high level of observance; but noticing by itself may not help explain what you are seeing. You may have noticed that your follow players are placing bets in apparently pre-determined positions; they go to them so quickly, that it seems that they have a pattern. They don't; what you are seeing are Called or Announced Bets.
These types of bets are according to the wheel and not the range of numbers it contains. For example if you bet on 1st 12 on the table you are betting on numbers 1-12, even though those numbers don't appear on the wheel in that order. A Called Bet enables you to bet according to the sequence in which the numbers are set on the wheel itself.
Called Bets are used on single-zero tables only and are particularly popular in UK and Europe: There are a number of different types, but the 3 main Called Bets are Voisins du Zero, Tiers du Cylindre, Orphelin.
Voisin du Zero: This 'Neighbors or Zero' bet, refers to the top section of the wheel if 0 is at the top. The range is from 22-25 inclusive and so the full bet covers 22, 18, 29, 7, 28, 12, 35, 3, 26, 0, 32, 15, 19, 4, 21, 2, 25. All of these numbers can be covered by placing chips in the following 9 position on the table; 2 on the 0,2,3 Street; 1 chip over the 5 and 7; 1 over the 12 and 15; 1 over the 18 and 21; 1 over the 19 and 22; 2 on the corner of 25, 26, 28 and 29, and one over the 32 and 35. So in total there are 2 chips on streets, 5 on splits and 2 on a corner.
Tier du Cylindre: This section is the one directly opposite the 0 but including less numbers; the Tier runs from the 27 to the 33 inclusive, which comes out as 12 numbers. These may all be bet on by placing chips in the following 6 splits; 1 chip on the 5 and 8, 1 on the 10 and 11, 1 on the13 and 16, 1 on the 23 and 24, 1 on the 27 and 30, and finally 1 on the 33 and 36.
Orphelin: The Orphans bet refers to the numbers left over on the sides of the wheel not included in the Tier or the Voisins. These add up to 8 numbers; 17, 34, and 6 from the right side, and 1, 20, 14, 31, and 9. All of these numbers can be covered by 5 positions; a straight up bet on 1, and then split bets on 6 and 9, 14 and 17, 17 and 20, and 31 and 34.
It sounds far more complicated than it is; once you're aware of the concept you will notice it in action more frequently, and see the value of its logic.