To create a truth table, first consider the number of individual variables being evaluated -- this is your initial number of columns. Next consider your rows: If you let x equal the number of variables, you will need 2^x rows for truth values (not including your header row identifying the variable and/or compound statement). Finally, when entering the truth values for each variable, starting with the first column, alternate T's and F's in groups of 2^x-1, decreasing x by one for each successive column.

Suppose you are working with 3 variables; p, q and r. Letting x = the number of variables, you will need 3 columns (x = 3), and 8 rows (2^x = 2³ = 8) for truth values. Now to enter the truth values: Starting with p, alternate with 4 T's and 4 F's (2^x-1 = 2² = 4), then alternate by 2's for the q column (2^x-2 = 2¹ = 2; starting to get the picture?), and finally alternate every other row with T and F (2⁰ = 1) for the r column, so that your truth table now looks like this: