What you are actually practicing
A1, B2, C3 is not one pattern. It is two sequences printed on top of each other: letters counting up, and numbers counting up, each at its own speed. Reading it as a single pattern is what makes it look hard.
The skill is separating channels: notice that two independent rules are running, solve them separately, then recombine.
How the game works
You are shown four or five letter-number pairs and four candidate pairs. Pick the one that comes next. A wrong pick reveals it immediately.
Easy has both channels stepping by one. Medium makes the letters jump by two while numbers still step by one. Hard makes both jump.
The relationships worth knowing
Same speed: A1, B2, C3, D4 → E5.
Letters jumping, numbers not: A1, C2, E3, G4 → I5.
Both jumping: A1, C3, E5, G7 → I9.
Strategies that actually raise your score
Read the letters only, ignore the digits. The letter channel is a plain alphabet sequence, and solving it alone already narrows the options to those starting with the right letter.
Then read the digits only. Any option with the wrong letter is already out; among the rest, only one has the right number.
Never compare whole pairs. Comparing C3 to E5 as units hides the two simple steps inside. Split them first, always.
Use the number channel as a tie-breaker. When two options share the correct letter — which happens on the harder levels — the digit decides it in one comparison.