From White belt to Master, here are a few of the best tips.

1. Reply to an email by chat-
If someone sends you an email, you can see whether or not they're signed into gchat when you view the email-

(I replaced subject title and contact name with stickers.)

Note the "Reply by chat" option next to the heart sticker. Also note the green dots that signify the person who sent you this email is online. Click on the link and reply to them in real time vs. email.

2. Search Mail-
Looking for a specific email from a pal? Dreading sorting through each and everyone? No worries. Just type in a keyword from said email, click on "Search mail" and get your results. Makes looking a lot easier.

You can also type in a search and click on "Search the web" which will take you to Google results without navigating away from the page.

3. Organize your email with labels-
Labels do the work of folders, plus you can add more than one to a single message. Give important emails brightly colored labels, and you'll be able to scan your inbox and quickly find the good stuff.

4. Gmail Voice and Video Chat-
Talk to people online so they can see/hear you. If you don't have a webcam, voice chat will still allow you and your friends/family hear one another.

5. Forgotten Attachments-
Mean to send an attachment with that email but forgetting to do so?
If you mentioned adding an attachment, and have the "Forgotten Attachment Detector" enabled in Labs, you will get an alert telling you you've left out the attachment upon hitting the send button.

6. Make Gmail go where the internet doesn't-
With offline Gmail, you can access your mail and use Gmail just like you're used to, even when you're not connected to the internet. Any messages you send while offline will be placed in your outbox and automatically sent the next time Gmail detects a connection. Get started by turning on offline Gmail from the Labs tab under Settings.

7. Sign out remotely-
Did you sign into Gmail from work then go home and think- "Darn it I forgot to sign out from my work computer! What if my boss goes snooping!?" No worries. At the bottom of your page you will see this:

Click on "Details" link (pink arrow is pointing to it) and it will open up a pop up that will let you know if you are signed in at another location. You will have the option to "Sign out all other sessions". This is also great for those people who's accounts are being hacked into. Not only can you see if you're logged in another location, you can see the most recent activity on your account by IP address.

These are all pretty basic things. There are many, many other tips to be found. So go to your inbox, click on the link and get better acquainted with all that Gmail has to offer.