Take pentane:

C₅H₁₂ + O₂ ->   CO₂ +  H₂O

Step 1 balance carbon:  you see 5 carbons on the left so you know it will produce 5 CO₂.

C₅H₁₂ + O₂ ->  5 CO₂ +  H₂O

Step 2 balance hydrogen:  you see 12 hydrogens on the left so you know it will produce 6 H₂O.

C₅H₁₂ + O₂ ->  5 CO₂ +  6 H₂O

Step 3 balance oxygen:  you see 10+6 or 16 oxygens on the right so you know it will require 8 O₂.

C₅H₁₂ + 8 O₂ ->  5 CO₂ +  6 H₂O

Wow!  It is balanced!
Actually, it doesn't always work out that easily.  Sometimes you get an odd number of oxygens on the right which leads to a fraction in front of O₂.  You then have to multiply all of your coefficients by 2.
(Vocabulary:  The numbers subscripted we have been calling subscripts.  These are the formulas of the molecules.  The numbers in front of the formulas (8, 5 & 2), are called coefficients.  These are the numbers we determine when balancing equations.)

Your steps are:
1) balance carbon
2) balance hydrogen
3) balance oxygen
4)  Multiply by 2 if you have a fraction.

Lets try a harder problem, hexane:

C₆H₁₄ + O₂ ->   CO₂ +  H₂O

Step 1 balance carbon:  you see 6 carbons on the left so you know it will produce 6 CO₂.

C₆H₁₄ + O₂ ->  6 CO₂ +  H₂O

Step 2 balance hydrogen:  you see 14 hydrogens on the left so you know it will produce 7 H₂O.

C₆H₁₄ + O₂ ->  6 CO₂ + 7 H₂O
                  (6x2=12 oxygens)   (7x1=7 oxygens)
Step 3 balance oxygen:  you see 12+7 or 19 oxygens on the right so you know it will require 19/2 or eight and a half O₂.

C₆H₁₄ + 19/2 O₂ ->  6 CO₂ + 7 H₂O

Step 4  To get rid of the fraction, we multiply all the coefficients by 2.

2 C₆H₁₄ + 19 O₂ ->  12 CO₂ + 14 H₂O

Ta da!!  Wow, it sure seems like a lot of work but it is really easy.

Try your hand at it at Dr Wong's website.