Mabrok, To begin with, read filter fundamentals from Textbook such as Microwave Engineering by Pozar. You will see how the S-parameters of filters look like. Also, if your project is an academic one, use a cheap FR4 material for your first design.
Later, you may go through more thorough book such as "Microstrip Filters for RF / Microwave Applications by Hong/ Lancaster".
Choose a permittivity where length of resonators fits your available board size. Higher permittivity results in smaller pyhsical size.
Look for small tolerances in permittivity if your filter is narrow band.
Look for small dielectric loss tanget, because that reduces insertion loss.
For the substrate height, look at gap width. Thinner substrates result in narrower gaps, which might be difficult for manufacturing tolerances.