Let a,b,c,d be coefficients in the balanced reaction.
a C₆H₁₂O₆ + b O₂ → c CO₂ + d H₂O
Count the atoms appearing on either side, and set the counts equal to each other for each element:
C : 6a = c
H : 12a = 2d
O : 6a + 2b = 2c + d
Let a = 1. Then
6a = c ⇒ c = 6
12a = 2d ⇒ 2d = 12 ⇒ d = 6
6a + 2b = 2c + d ⇒ 6 + 2b = 2•6 + 6 ⇒ 2b = 12 ⇒ b = 6
So, the balanced reaction is
1 C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O