(a) Consider the physiological changes that occur with aging. You may also consider co-morbidities and number of medications.
Relevant examples:
E.g., ALP (for liver function tests)
Age: levels are elevated during childhood/puberty and rise again in old age.
M/F: ALP is elevated in males more than it is in females (between 15-50 years). But can be higher in females during late pregnancy and perimenopause.
E.g., Total cholesterol, triglycerides, and LDL levels
Age: increase with age.
M/F: increased in males until 50-60 and 60-70 in females. But triglycerides may remain high in older females.
F: consider pregnancy --> AFP, blood volume, lipids, creatinine clearance, ESR, estrogen, testosterone, progesterone, prolactin, hCG, transferrin levels, WBC count: increases. Hemoglobin, ferritin, FT4, TSH, prothrombin, partial thromboplastin time, sodium: decreases
(b) Consider low and high body weight and how it can affect body function
Relevant examples:
E.g., obesity results in greater BMI and PSA levels. It can also increase CRP and ESR - think about how this may affect the diagnosis of Rheumatoid Arthritis.
-Considering the above, what could you deduce for an underweight individual?
(c) Consider: calorie restriction, fasting, malnutrition, dehydration, and food exclusion diets.
Relevant examples:
E.g., ensuring sufficient gluten levels in diet prior to Coeliac Disease investigations.
E.g., Assessing dietary factors: A vegetarian/vegan diet can result in decreased vitamin B12 levels. A low-carb diet can increase ketones. A high-protein diet can increase uric acid levels. E.g., Fasting before tests such as for: creatinine tests (any recent meaty meals can influence creatinine which you could consider when monitoring eGFR), you may or may not require someone to fast for tests regarding uric acid, glucose, or triglyceride levels.
More examples: dehydration --> can cause a potassium/sodium imbalance, affecting lipids, albumin and urea. Malnutrition --> can affect vitamin B12, ferritin and folate levels. Starvation --> can affect glucose, electrolytes, lipids, thyroid function, liver function, and renal function. Alcohol --> decreased glucose, decreased uric acid excretion, increased lactate levels. Chronic alcohol consumption --> increased GGT, MCV, AST, ALT, triglycerides, uric acid and ferritin.
(d) Laboratory parameters differ based on the time of day, week, month, or year taken. Body temperature, testosterone, cortisol, cognitive, platelet and cardiac function follow a 24-hour rhythm.
Relevant examples:
E.g., It's recommended to test testosterone from 7 am-10 am.
E.g., cortisol: recommended sampling levels early in the morning.
E.g., vitamin D levels: interpreted based on time of year. A deficiency during winter may be less significant than during summer.

For more detailed descriptions I'd recommend searching over on "Cleveland Clinic"! Best of luck:)