Understand the process. "Gibberish" is an umbrella term for any nonsensical language that is hard to understand, such as baby talk. However, all established variants use the same pattern: A nonsense sound is inserted into every syllable when speaking. The same nonsense sound is used over and over, so words get much longer and all sound quite similar.
Break a word down into spoken syllables. Generally, every syllable in a word contains one vowel sound. Here are some words and their syllables:
Add "-othag-" before each vowel sound in a syllable. If there are only vowels (e.g., "I"), add it at the very beginning. Regardless of whether there are 1,2, or 3 consonants at the beginning, add it before the first vowel sound. The result will sound something like this:
Resist the urge to repeat vowel sounds. If you were to say the word "hi" in gibberish, it may be tempting to pronounce it "hi-tha-gi," instead of "ho-tha-gi." Don't do it! It's harder to decipher when you add in a different vowel sound.
Repeat, repeat, repeat.Eventually, it'll seem like othagold hothagat. You'll grow more and more confident, shortly moving onto phrases and sentences. Take a look around your room. What objects do you see?
Get quicker. After a bit of practice, the words will start rolling off your tongue. Try reading aloud the words on this page in gibberish. How quickly can you translate? Are you ready for sentences?
Experiment with different variations. There are many established variants, and you're completely welcome to come up with your own twist -- though no one else will understand you. When it comes to that inserted sound, here are some possible (already established) variants:
Practice! Get out a few old baby books and read them out loud in gibberish. Keeping the three syllable words to a minimum (how did you do with Gothagibbothagerothagish above?) is key. Once the baby books are easy, it's time to impress your friends!
Use your powers wisely. Now that you can say whatever you please in front of anyone, don't abuse your power. After a few phrases, you're going to be like that guy that has a French word for everything. People may get irritated, especially if you don't tell them what the heck is going on. If you'd like, you could teach them your ways, but it may be more fun to see if they can figure it out first.