If your clutch operation begins to feel heavy, stiff or no longer smooth then it could be an early sign that your clutch has become defective.
When under load i.e. when travelling up hill or under acceleration your engine revs rise or a strong burning smell occurs then this could be a sign that your clutch is excessively worn.
Clutch operation under normal circumstances should be light, smooth and noise free. Changing gears should be smooth, easy and without excess effort (or any crunching noises). If it's not, let us check it out for you.