There are 4 days yo can progressively overload.

-Increase resistance

Resistance refers to the stress placed on a muscle by gravity (or weights). Resistance can be increased by adding more weight to your workouts as you progress every week. You should be able to perform 10-12 repetitions with proper form before you consider adding more weight to a workout. 

For example:

Week 1 you perform a set of squats for 10-12 reps with good form using 100 lbs and then do the same for week 2. By the start of week 3, you should be progressing by adding 2-10 more lbs to your squat depending on how you’re feeling until you are able to successfully perform 10-12 reps using that new weight. 

-Increase endurance 

For cardiovascular-related workouts such as sprinting, running, or any movement that involves a static hold such as a plank, wall sit, or handstand, you can progressively overload by increasing the time under tension (length of the workout). This will allow your body to experience resistance from gravity for a lengthened period and lead to successful progressive overload.

For example:

If you’re starting a workout program and on week 1 the program asks you to perform 4 sets of planks for a duration of 30 seconds each, by the second or third week you should be able to progressively add more time under tension and perform that movement for a static hold of 45 seconds.

-Increase tempo

Tempo refers to the pace at which a movement is performed at different stages. Tempo consists of 4 numbers. These four numbers are used to help break down each of the different phases of a single repetition. This includes the eccentric (muscle lengthening under tension), contraction (muscle shortening under tension), and the pause between each of these contraction types.

The first number relates to how many seconds you take to lower the weight (eccentric phase). The second indicates how long you should hold the weight in a pause at the bottom of the movement, the third number represents the time taken to lift the weight to the original starting position (the contraction phase), and the fourth number is how long you should pause with the weight at the top of the movement.

An example would be 

4020 TEMPO SQUAT:

4 - Take 4 seconds to squat down (eccentric phase)

0 - No pause time at the bottom of the movement

2 - Take 2 seconds to rise up to starting position (concentric phase)

0 - No rest at the top of the movement

By changing your tempo in the eccentric or concentric phase you can manipulate the resistance being applied and thus progressive overload. 

-Increase reps

Adding more reps also allows you to progressively overload. You can focus on performing a set amount of res on your first week then add more reps for the second or third week. 

For example:

On week 1 you perform 2 sets of 10 reps for bicep curls. You then continue to add more reps and by week 2 you perform 2 sets of 12 reps instead. This is one of the safest ways to progressively overload without adding more weight to your workouts.