Are you choosing a body weight exercise and finding it somewhat easy to complete the desired repetitions along with correct tempo? Is it time for you to increase the resistance?
When you perform bodyweight exercises such as pull ups, press ups or dips you are working against your own bodyweight which is considered to be weight training. That’s right, so you don’t technically need weights to be weight training, many bodyweight exercises are much harder than those with a dumbbell. Over time you will find in any weight training exercise you’ll gain strength and the ability to increase the load. A simple progression for pull ups would be to use a weighted vest, or placing a dumbbell between your legs or hang some weight from your waist with a chain. A progression for press ups could be to use resistance bands to increase the resistance on the push, or use a weighted vest or even place a weighted plate on the back. A simple progression for dips can be to again use a weighted vest, chains or place a dumbbell between your legs.
Selecting how much load you can increase will vary from person to person, but... Your main focus should be to only progress in load when your finding it easy with good movement quality.
Personally I like to play on angles before I choose to increase the weight. For example, press ups with feet elevated on a bench, I’m challenging the movement by adding a new variety of stimulus and stress to the targeted area. Pull ups I would suggest attempting a body row, this is where you would grip the bar at waist height with the feet resting on the floor whilst attempting to pull the chest to the bar. Dips I would suggest using dip bars and switch your leaning position. Many don’t consider which way they are leaning as they have started from what feels comfortable/natural and stuck with that position. So the next time you perform a dip look at where your shoulders are, do the stay in front of the chest, at the side or behind?
If you are looking to build a much stronger core then stick to bodyweight exercises rather than sitting a nice comfy chair on a resistance machine.