I have been through all this process let me tell you a detail overview about what all is there
All the tests are given on a website named Hawinfo as well
The first thing which you will be doing there is a lot of form filling. try to write the same things in all the forms because you will be asked to fill more than 2 forms there.

Then comes the address by commandent ISSB. The very 1st day there are intelligence tests. You can find some exercise which are relevant to the tests here
After the intelligence test is done you will be doing mechanical aptitude test which includes some easy questions from physics.
The next things is psychologists tests which are the main crux of ISSB. this includes tests such as
Sentence completion English. You will be given two papers which contains 26 incomplete sentences in English and you need to complete them in 6 minutes. You can find some examples here
Next is the sentence completion in urdu. Here you have the same thing 2 papers of 26 incomplete sentences and the time is also same. find some useful examples of the test here
then you will be shown 2 pictures on a projector now you have to write stories on these pictures. Make sure you right a positive one. Some example stories are solved here read them
Next comes word association test now you will be shown some 100 words and each word will be displayed for 10 seconds you have to make sentence on it during that time....See some useful exercises here
the last test in the psychologist is pointer stories writing ....An incomplete story is given and you need to solve it...See the exercises here
There are 2 interviews in ISSB one by Deputy, and one by psychologist. Psychologist interview is based upon you psychological tests for Deputy and psychologists Interview watch the questions here
then you have many physical tasks which are monitored by group testing officer read them full here
if you want to ask anything feel free to ask