Proofs are assigned point values between 0 and 4 as follows.
4 Points: Perfect. Would pass an automated proof checker.
3 Points: One or two minor misapplications of rules that could easily be fixed by being more careful. For example:
1 (1) P->-Q A 2 (2) Q A 1,2 (3) -P 1,2 MTT
For full credit, there must be an additional line:
1 (1) P->-Q A 2 (2) Q A 2 (3) --Q 2 DN 1,2 (4) -P 1,3 MTT
2 Points: The proof includes one or more successful substrategies, but has irremediable flaws. (This is mostly applicable to complex proofs.) For example, having a "false line" (i.e., the sentence on the line does not follow logically from its dependencies) is usually an irremediable flaw.
1 Point: Some correct applications of the rules, but no proof strategy is apparent.
Check your dependency numbers carefully. Mistakes in dependency numbers will cost you points.