Starting testing a new project

Hi everyone! I am working as manual QA engineer in startup company. We are working on several project at the same time and currently are developing a new Web application for one of our clients.
Can anyone give me some tips on how to build a right QA approach for testing new application? It will be delivered to me in pieces as development goes.

Creating a proper test plan and understanding the system is definitely #1 point.

What is the best way to plan cross-browser / device testing ? Any tools / materials you can recommend ? What else am I missing ?

I will highly appreciate any callouts and if you could share your personal experience.
Thank you !

Welcome to the community Viola.
I’m gathering that you are working for a “consultancy”, I.E. writes apps and sells or licenses the final thing, and then starts a new app 6 months later and totally forgets about the last app we sold?

A few of the folk in the club work on such companies, I hope they can help us here with survival tips. If it were me, I would be just jumping into every single requirements meeting, and just listening-in, every single defect triage meeting too, and mostly just trying to pace myself and not burn out.

How frequently do you switch project? And then use that in deciding what kind of re-usable planning templates and finding heuristics that apply consistently to every project will help.