Sometimes I realise while composing a message that I'd like to star the resulting conversation. Currently I wait until I've finished writing and sent it, open sent items, then star the conversation. Is there a quicker way or perhaps a way to star it while I'm still composing?
I believe your only option while composing your new email is to click "Drafts" on the left, star your draft, then click the draft open so you can finish it.
Or you could create a filter for "email@example.com" and bcc it to this email address. The filter would then just star any emails that have bcc = this email.
You have three options that I can see without dropping out of your message editor:
1) Jump the editor out of the first browser window into it's own browser window
If you are in the message editor you can click on the icon the upper right corner (looks like two offset stacked boxes) that opens the editor in a new browser window. (You can even do this in mid-edit. It will copy everything you have typed into the new browser window)
Once the editor is in a new browser window, you can jump back to the first browser window and browse other emails, star messages and conversations and do any mail management that you need to do, all while continuing to edit your message in the second browser window.
2) You can actually star each message in the conversation while you are doing the editing of a reply. The star icon is available in the upper left corner of each message in the conversation.
3) You can click on the "more Actions" menu and choose "Add star". The more actions menu is at the top of the conversation thread on the message action toolbar.