On a homepage, a Welcome message contains no information and is a massive waste of very valuable screen space. The way to welcome your visitors online is to provide information that shows them exactly what you're about and how you can help them.
2. Please and thank you
These too are pointless pleasantries on a website. Crisp clear instructions that tell user where to go on your site and what they'll find when they get there are the real courtesy online.
3. Click here
Wrong from every point of view. Bad accessibility because meaningless to people using screen readers. Hopeless for scan readers who 'may' just be looking at signposting copy such as heads and links. And a wasted seo opportunity - google looks hard at anchor texts, and this one contains no keywords.
4. Retrieve a quote
No one uses this sort of language in the real world. What's wrong with something plain like - Return to your quote?
5. Mandatory fields
Robotic data-capture speak. In any other context these would be boxes. And we'd just say you must fill them in.
6. Check this box
In British English at least, people tick boxes or put crosses in them.
7. Library / Resources
This tends to refer to the area of the site that should be really called: "dumping ground for pdfs and other bumpf we couldn't think where else to put but were told had to go up somewhere".
When used in headings and tabs, as in "Other news", "Our other products" etc. Other to what? These labels are unscannable because the information they convey is not self-contained - they rely on the user looking at something else to make complete sense of them. Which doesn't work well online, where you cannot fully control the context in which people see your content or even the way it's presented.
Meaningless marketing hype. What sells online is real, specific information. Telling me your product or service is unique tells me nothing.
Some websites still arrange their content into editorial buckets like "features", "news", "events". Fine for organising your content internally but don't let these labels make it on to the site, where they'll mean nothing to your readers.
An SEO specialist recently told me that if he could ban one word from websites, this would be it. Everything is described as a solution nowadays, from sandwich bars to industrial cranes: Private Eye even has a column where people send in their favourite dire examples. But only businesses call their products and services "solutions" - their customers never do, which is bad news from both an SEO and plain language/usability point of view.