The real answer is: "any chord you want comes next." That may sound glib, but it isn't. Sure, there are convention chord changes, and you can use those conventions to say "what should come next," but you can intentionally play against conventions for effect, to surprise, or venture off into distance areas in a large composition.
From a conventional point of view...
The verse chord progression is : G, Cadd9, A7sus4 and Dsus4
You can analyze that as (simplified)
I IV V7/V V. That is pretty conventional. You have a tonic chord, pre-dominant harmony, and then the dominant. You could paraphrase that as just
I made a bridge with Em7 and Bm7
vi or going to the relative minor. That's very conventional for a bridge or middle eight.
In terms of harmonic contrast going to the relative major or minor works, because you change the mode/quality and get a different mood.
But a bridge should also go somewhere. It's a bridge to something. The bridge first provides harmonic contrast, then it goes to some other tonal space. A conventional thing to do is play the dominant chord of wherever you are going, or some progression to the dominant in the key you are going to. If you are going back to
G try playing
D to conclude the bridge.
Assuming a return to
G and an eight bar bridge you could try some things like:
|Em7|Em7|Am|C D7| ...to
Notice the variation in endings, but they all end on the dominant of
G. Using a dominant chord is a very conventional approach to change or return to a tonal area. It's not the only way to do it, but it's common.
On the other hand you could do something more unconventional, like...
...a digression into a totally new place:
You can play around with the specific chord extensions and voicings, as well as how many bars to hold a chord. You have latitude to try various options in that regard. But what you really want to ask about the bridge is where do you want it to take you harmonically?
...How can I improve my knowledge about chord progression and make interesting chord progressions...
There isn't really a short cut to understanding. The thing to do is analyse the chord in lots and lots of songs. Ideally you should find a library with a good music score collection and look for songbooks. Combine song analysis with studying a good harmony textbook (like Kostka, Tonal Harmony. or some other college level book.) The important point being it takes time to develop deep understanding rather that just cobbling together common progressions through trial and error.