I was like you once. After fetching my e-mail, I'd open a message I wanted to delete, tap the trash-can icon, go back to the in-box, open another message, tap the trash-can icon, and on and on.
Then I discovered a killer shortcut: From the in-box, just swipe your finger across the message you want to trash, and then tap the shiny red Delete button that appears. Talk about a time-saver!
You can wipe multiple messages even faster by tapping the Edit button in the top-right corner of the screen, tapping each e-mail you want to mark for deletion, and then tapping the lower-left Delete button.
By the way, if the Mail application isn't showing you enough of each message to decide whether you can pitch it without opening it, there's an easy solution: Head to Settings, Mail, Contacts, Calendars, then tap the Preview button in the Mail section. Two lines is the default, but you might want to bump it up to three or four so you can see more of each message.
Got an e-mail tip of your own to share? Share your wisdom with us in the comments.