Speed is a requirement, not a finishing touch
How heavy a page is gets decided while you build it, not at the end with a
plugin that promises to fix it. How many images you load and how, how
much code you make people download, how much work you ask of the phone in
their hand: those are design decisions, and taken late they are not taken at
all.
Page weight · Images · Shipped code
Accessibility is not a box to tick
A site gets used with a keyboard too, with the text zoomed in, on a beach with
the sun on the screen. Writing HTML that says what things actually are, and
not only how they look, is the difference between a site people can use and
one that only looks good in a slide deck.
Semantics · Keyboard · Contrast
Somebody else has to read your code
On a team, what you write immediately becomes somebody else's problem. Clear
names, conventions you follow, no clever shortcuts that even you cannot decode
six months later. That is the difference between a project you can maintain
and one held hostage by whoever wrote it.
Conventions · Review · Naming
Measure first, argue later
In a place like that, opinions about what works better last as long as it takes
to open the data. Tests before release, measurement afterwards, and the
willingness to find out you were wrong. It is the most uncomfortable habit, and
the most useful.
Tests · Measurement · Checks