When installing the back-end and especially the front-end framework make sure they are in line with the needs and principles determined in the Design phase.
As the designs, wireframes and mockups were based on a certain framework (Bootstrap, UIkit, Foundation etc, etc.) it’s wise to also implement these in the first step. This makes the whole process a lot more efficient for all and will everybody ‘speak the same (front-end) language’.
Make sure to setup all (indirectly) related systems like a repository, the testing server (preferable on the target server), pipelines, domains and eventually IP blocks - so the focus in the next step can be completely on the development of the actual product. Communicate with the client what’s relevant to keep the process efficient - not too early - and definitely not too late, keep it clear and always be honest.