I've seen this on Pintrest and also here. So it's not really my idea but I'd like to show you what I did if that's ok :-)
You will need:
A plain ceramic mug, dishwasher and microwave safe.
(I told you it was easy!)
Draw your design all over your mug. I'd recommend not drawing on the parts that are going to touch your hot drinks. I chose a sweet heart pattern but you can find ideas everywhere. How about a quote you love? Or copy your kids drawing? Or get your kid to draw on it, that would make a fun present for a grandparent!
I didn't do the handle - this isn't a totally fool-proof method and the handle will...get held a lot. Ha. So I thought the design might rub off and also, drawing on the cup was quite tricky. I found the best position was rest the cup on my knee with my left hand flat over the top holding it in place. Try not to touch the design as you move round the cup because it will rub off quite easily or smudge.
If you make a mistake, use a teeny amount of hairspray on a cotton bud (q-tip) to clean up the error.
Put your finished cup in a COLD over and turn the heat up to 300. Leave for 30 mins. Putting it in cold should prevent the mug cracking in the heat but this is why it helps to have a microwave safe mug in the first place.
Open the oven door, turn off the heat and let the cup and oven cool down completely before removing and making yourself a nice brew :-) Hand wash your mug only. The design should stay on, but it will depend in the glaze/coating of the mug you used.
Please feel free to comment if you have any questions! I was super-happy with the comments on my mermaid manicure post yesterday, so thank you for reading *waves*