A successful cut (fat loss phase) requires a calorie deficit while creating the nutritional conditions that preserve muscle mass. The primary threats to muscle during a cut are: insufficient protein (providing inadequate amino acids for muscle protein synthesis), too large a calorie deficit (causing catabolism of muscle tissue for energy), and reduced training intensity (removing the stimulus that tells your body to maintain muscle).
Cutting nutrition setup: Set calories at 300-500 below TDEE. Set protein at 2.2-2.6g per kilogram of body weight - higher than in a surplus because protein turnover increases in a deficit and dietary protein must compensate. Fill remaining calories with carbohydrates and fat in a ratio that supports your training performance and satiety. Generally, keeping carbohydrates reasonably high (supporting training intensity) and fat moderate works well.
Rate of fat loss: aim for 0.5-1% of body weight per week. Faster than this increases the risk of muscle loss. For an 80kg person, 0.4-0.8kg per week is appropriate. If you're losing faster, add 100-200 calories. If slower and you're not satisfied with progress, remove 100-150 calories. Maintain your training intensity and load during the cut - lifting heavy is what preserves muscle. Reduce training volume slightly if recovery is suffering. A cut should typically last 8-16 weeks before returning to a maintenance or surplus phase to allow hormonal recovery and performance restoration.