Think of two existing words and squish them together to form what is called a portmanteau word. "Brunch" is a classic portmanteau that combines the words "breakfast" and "lunch."
Stick a prefix onto a word you already know. Latin and Greek roots are a great starting point for inventing new pseudoscientific words.
Listen to the sound of your word and the personality it expresses. Invented words should reflect the character of the things they describe. For example, "bodacious" evokes a feeling of fun, excellence and attractiveness.
Stick suffixes on the ends of well-known words. Although it's not exactly a suffix, the "-holic" part of "alcoholic" sounds good with other addictive behaviors, such as "chocoholic" and "spendaholic."
Invent a catchy, one-syllable word with an ambiguous meaning. "Darsh" is a good example. Although such words are easy to remember, they're also flexible--their meanings are so abstract that you can use them in almost any context and sound good.
Use your new word often and in different contexts. The more exposure your word gets, the more likely your friends and family are to pick it up and spread it around.