Design pattern user <--> server <--> MySQL

I'm a beginner having some experience in python, java, sql etc. I'm currently learning PHP and am about to create a website where the user can fill out a form to filter houses of interest. Parameters could be "Area", "Size", "Price", etc and theses parameters will then be sent to a MySQL database and a result depending on what's in the database will be shown to the user.

My biggest issue when writing code is that I'm too unstructured and don't plan ahead, rather I just start coding sequentially and often find myself lost in bad code.

I would be very thankful if anyone could advise on how I should attack this project in terms of what design pattern to use, what classes and what each class should be responsible for OR just advise on a webpage where I can read up more on this.

Many thanks!