How to Open a Tight Jar
To open a tight jar, start by wrapping a towel around the lid to get a better grip, and twist the lid open. If that doesn't work, put a piece of plastic wrap around the lid to make the lid sticky, or put on a pair of rubber gloves. To break the vacuum seal of a jar before you open it, tap the blunt end of a wooden spoon forcefully in 6 places around the edge of the lid to make air bubbles before you twist the lid. If that doesn't work, run the lid under hot water so it expands slightly, then try turning it!
Wrap a rag around the lid and twist before trying anything else. Jars are usually pretty easy to open once you can get a good grip on it. Wrap a thin rag around the top of the jar. Then, wrap your stronger hand around the lid and twist anti-clockwise as hard as you can. The increased grip from the rag should make twisting the lid off much easier. Put an elastic band on the lid if the rag doesn't work. An alternative method of getting a grip on the lid is using an elastic band. Stretch an elastic band around a lid so that it grips all the sides tight. Then, use your dominant hand to twist the jar anti-clockwise. Your hand will be able to grip onto the elastic band as you twist, making the jar easier to open. If one elastic band doesn't do the trick, you can wrap several around the lid for more stubborn jars. Layer plastic wrap over the lid to get lots of grip. Layer a large sheet of plastic wrap over the lid so that it's completely covered. Grip the lid with your dominant hand, letting the plastic crumple inwards towards the lid. Then, twist anti-clockwise as hard as you can. The plastic wrap will grip to the moisture in your hand. The more grip you have, the easier it is to twist a lid off a jar. Once you get the lid off, layer plastic wrap over the jar before putting the lid back on. This will make twisting the lid off much easier next time you need to. Wear rubber gloves if you have them before twisting the lid open. Wearing rubber gloves to open a lid has a similar effect to layering plastic wrap over a jar. But rubber gloves are more flexible as you can grip the lid in whichever way is more comfortable for you. Grip the lid as tightly as you can with your dominant hand and twist anti-clockwise. The rubber gloves will give you more grip on the lid, making it easier to twist open. Tap the lid with a wooden spoon first. Put the closed jar on a flat surface. Grip a wooden spoon in your dominant hand. Pick 6 evenly-spaced spots around the circumference of the lid and tap them firmly with the head of the spoon. Then, try to screw the lid off with your dominant hand. It should be easier to twist off. Tapping the edge of the lid causes air bubbles to rise, loosening the seal of the lid. Use a bottle opener to pry open the lid if you've got one nearby. A bottle opener will usually have a hooked edge to pry under the lids of bottles. Jam the hook under the lid of the jar and pry it upwards. If you hear an audible hiss you've managed to break the air seal. Twist the lid off with your dominant hand. Rinse the lid in hot water if you don't have other tools. Put the lid of the jar under a stream of hot water and slowly rotate it for 1 minute. The hot water will expand the molecules of the lid, making it easier to pry off. After the minute is over, dry the jar. Hold a rag in your dominant hand and use it to screw the lid off. If you don't have a source of constant hot water, you can make a hot water bath instead. Fill a large bowl with hot water. Then, invert a jar and plunge the entirety of the lid into the bath for a full minute. Take the jar off, dry it with a rag, then twist anti-clockwise with your dominant hand to open the lid. Smack the bottom of the jar with your hand to create air bubbles. Hold the jar by the lid at a 45-degree angle with your non-dominant hand. Stretch your dominant hand out, then smack the bottom of the jar firmly with your palm. This force should send air bubbles up towards the lid. You may need to smack the bottom of the jar several times to get the desired effect. Tap the bottom of the jar against a table if smacking it doesn't work. With your non-dominant hand, hold the desired jar at a 45-degree angle from the lid. Then, using the edge of a firm surface such as a counter or table, tap the lid against the edge. This will send air bubbles up through the jar which will help break the air seal. Do not tap the jar too hard. You can risk damaging the jar or even breaking it. Use an open flame to heat up the lid as a last resort. Do not try this method if you are not an adult. Hold the jar by the bottom and lower the lid towards an open flame. The flame of a gas cooker works best. Slowly rotate the lid around, letting the flame heat up the lid. This process shouldn't take more than a minute. If you see the lid start to bubble or drip, immediately remove it from the heat. This heat, much like the hot water, expands the molecules making it easier to open. Make sure to open the lid with a thick rag or gloves after heating it as you could accidentally burn yourself. Twist the lid counter-clockwise with your dominant hand. 
Wrap a rag around the lid and twist before trying anything else. Put an elastic band on the lid if the rag doesn't work. Layer plastic wrap over the lid to get lots of grip. Wear rubber gloves if you have them before twisting the lid open. Tap the lid with a wooden spoon first. Use a bottle opener to pry open the lid if you've got one nearby. Rinse the lid in hot water if you don't have other tools. Smack the bottom of the jar with your hand to create air bubbles. Tap the bottom of the jar against a table if smacking it doesn't work. Use an open flame to heat up the lid as a last resort. 