Be careful entering expressions just as you would be careful entering expressions in a calculator.
Sometimes using the * symbol to indicate multiplication makes things easier to read. For example (1+2)*(3+4) and (1+2)(3+4) are both valid. So are 3*4 and 3 4 (3 space 4, not 34) but using a * makes things clearer.
Use ('s and )'s to make your meaning clear. You can also use ['s and ]'s and {'s and }'s.
Don't enter 2/4+5 (which is 5.5) when you really want 2/(4+5) (which is 2/9).
Don't enter 2/3*4 (which is 8/3) when you really want 2/(3*4) (which is 2/12).
Entering big quotients with square brackets, e.g. [1+2+3+4]/[5+6+7+8], is a good practice.
Be careful when entering functions. It's always good practice to use parentheses when entering functions. Write sin(t) instead of sint or sin t. But WeBWorK is smart enough to accept sin t or even sint. But sin 2t is really sin(2)t, i.e. (sin(2))*t. Be careful.
Understand that sin^2t is really short hand for (sin(t))^2 and must be entered this way. Actually you could enter it as sin(t)^2 or even sint^2, but don't try such things unless you really understand the precedence of operations.
For example 2+3sin^2(4x) is wrong. You need to enter something like: 2+3(sin(4x))^2 or 2+3sin(4x)^2. Why does the last expression work? Because things in parentheses are always done first [ i.e. (4x)], next all functions, such as sin, are evaluated [giving sin(4x)], next all exponents are taken [giving sin(4x)^2], next all multiplications and divisions are performed [giving 3sin(4x)^2], and finally all additions and subtractions are performed [giving 2+3sin(4x)^2].
The complete rules for the precedence of operations, in addition to the above, are
Use the "Preview Button" to see exactly how your entry looks. E.g. to tell the difference between 1+2/3+4 and [1+2]/[3+4] click the "Preview Button".