Consonants where the articulators (parts of the mouth that you use to make sounds) can be seen are pretty easy to teach. For example 'F' and 'V' you make by touching your top teeth to your bottom lip and blowing air through through them. Consonants where the articulators aren't so easily visible are much harder to teach and require careful explanations, diagrams, and other teaching tools. This latter bit applies to vowels too but in my experience vowels are even harder to teach because the manner of production is difficult to describe in spatial and physical terms.
To teach the sounds of your language you first need to learn them. You might not realize all of the sounds you use in your language and your writing system might influence the way you think about those sounds as well. I advise looking up the phonology on the internet and saying the sounds and examples while you read through them. Learn how they're different from English. Focus on the differences but learn the similarities as well.
- Mid-sagittal diagrams (They show the vocal tract as if the head were sliced in two between the eyes)
- Mirrors (So your students can see their articulators moving while watching yours)
- Listening practice pyramids with minimal pairs
- A list of words that use the sounds that you can read through to exemplify the sound in different environments (context helps people learn!)
- If at all possible, videos/3d simulations of the mouth moving to make the sound
- A kazoo for teaching intonation or stress patterns
- These and more tips are available at http://writing.colostate.edu/guides/teaching/esl/pronunciation.cfm
Good question. A minimal pair is a pair of like words that differ in only one regard. For example "bad" and "bid" are minimal pairs. You could say that "bad", "bid", and "bud" is a minimal triplet. The important part is that the only thing different about these words is the vowel sound. The pronunciation is otherwise the same. Other examples are "cat" and "bat", as well as "mean" and "meal".
There are also something called near minimal pairs. These are pairs of words that differ slightly more, but not much. We can use near minimal pairs if there isn't a minimal pair to explain a certain sound. For example, in English "blimey" and "crimey" are a near minimal pair. They differ in the initial consonant cluster. A Japanese listener however would only realize that they differ in the first consonant. The "l" and "r" distinction isn't immediately perceptible by most Japanese learners of English. Thus if I needed to teach the difference between "b" and "k" (the sound 'c' makes here) I would need to use a different example if possible, because there are other potentially complicating factors. It's also not a great example for "l" and "r" because the first part of the consonant cluster is different.
Start off with simple, direct differences. Move towards more complicated ones once people have clearly mastered the simple ones.