Start with the regulations
Universities define their own appeal grounds. Common grounds concern a procedural irregularity, circumstances that affected assessment, or evidence that the decision was affected by bias. Read the policy that applied to the decision rather than assuming a standard form of appeal applies everywhere.
Connect the ground to the outcome
State what happened, which rule or safeguard matters, the evidence supporting it and how the problem could have affected the result. An appeal is usually stronger when it identifies a reviewable issue than when it asks a panel simply to substitute a new academic opinion.
Build a focused evidence pack
Keep the decision letter, regulations, relevant correspondence and documents showing dates and impact. If evidence is unavailable, explain what you have requested and when it is expected. Check whether the university requires a particular form or stage.