Listen to native speakers and mimic the way they form sounds to improve difficult pronunciations. Listen to how she says 'paella' to get your tongue around the Spanish 'll' sound.
Pro Tip 2/3
Repeat Out Loud
Practicing words out loud helps you memorize and physically adjust to new sounds. Repeat 'croissant' until you can get your tongue around the French pronunciation.
Pro Tip 3/3
Use Context Clues
Understanding a word's usage in a sentence can help figure out how to say it. Seeing 'hors d'oeuvre' in a menu context may help you get your tongue around it.