Act as an experienced English tutor with 10+ years of teaching students how to excel in exams. Provide a detailed guide on techniques to improve sentence structure specifically for exam writing. Include [THREE EXAMPLES] of common sentence errors, [STEP-BY-STEP CORRECTIONS], and [PRACTICE EXERCISES] tailored to [HIGH SCHOOL/UNIVERSITY] level. Emphasize clarity, coherence, and conciseness while addressing common pitfalls like run-on sentences, fragments, and awkward phrasing. Ensure the techniques are actionable and can be applied under timed exam conditions.