Here are 3 tips that should help you perfect your Chinese pronunciation of 愉快:

• Break 愉快 down into sounds: say it out loud and exaggerate the sounds until you can consistently produce them.
• Record yourself saying 愉快 in full sentences, then watch yourself and listen. You'll be able to mark your mistakes quite easily.
• Look up tutorials on Youtube on how to pronounce 愉快.

To further improve Chinese pronunciation, we suggest you do the following:

• Learn Pinyin: This is the official way in China of writing the sounds of Mandarin using the Western alphabet. Each syllable or character can be written out with a little accent above the letters to indicate 1st, 2nd, 3rd or 4th tone. Check out Yabla Pinyin Chart With Audio to see it in action.
• Speak to native Chinese: If you are able to speak to native Chinese speakers or a teacher, ask them to point out specific problems with your pronunciation.
• Subscribe to 1 or more Chinese teaching channels on Youtube: it's free and it covers the core topics of the Chinese language. Check out Katrina Lee, ChinesePod and Yoyo Chinese channels to name just a few.