Get students to practice saying each letter of the alphabet, primarily to allow students to become familiar with the sounds of each letter, but secondly to identify any particular problematic letters. It's important to recognize that letters are the building blocks of words, and by focusing on the smallest element of pronunciation, greater difficulties in word pronunciation may be avoided. For higher-level students, focus can be on specific words that are creating difficulty, but going back to the basics of individual letter pronunciation may still be required in given situations.
Observe where possible and listen for any problems with pronunciation. Remember, speaking English is something that is done instinctively for native speakers, and it can be taught. Tell students how you use your mouth for pronunciation during the process of pronouncing each word. Explain how you use your mouth, teeth and lips. Does your tongue touch your teeth? Do you purge your lips when speaking, or is your mouth fully open? With a little thought, most people can explain how they use their mouth when speaking. Get the students practicing, and listen to students individually.
Look at phonetic diagrams for any particular letters that may be difficult to pronounce. The diagrams show a cross-section through the mouth indicating the tongue, teeth and lips, and it's possible to explain the process of pronunciation using the diagrams as visual aids. What you may not be able to get across with words alone may be better explained with the use of diagrams. PDFs are a common way of sharing electronic image files.
Give electronic handouts to students with lists of words that you intend to practice in phonetic lessons.
For the words you are studying, indicate each syllable of the word with a hyphen or dot between each syllable. This will enable you to identify which syllables in the word should receive greater stress when speaking. Demonstrate to the students how dictionaries, either online or hard copy, can be used as pronunciation tools, because many dictionaries indicate the syllables of the words.
Demonstrate how the words you have are spoken by slightly exaggerating the emphasis of tone when speaking. Remember to take into account the time lag for Internet connections. Be methodical but not rushed.
Words are not expressed in flat tone, and by exaggerating intonation, students can clearly hear if tone is rising or falling across the length of the word. It's possible that this can be a group exercise to eliminate any inhibition problems initially in speaking, but each student needs to be heard individually to assess progress and comprehension.