But wait, there's more!

In the meantime, I realized that there are other consonants to work on! I read a bit more on Spanish phonology on Wikipedia and I also checked out other exercises on StudySpanish.com - here, the explanations on how the sound is formed are not always very good but at least there are clear examples. 

I found that I also need to improve: the  /b/, /d/, and /ɡ/, which are pronounced as approximants, unless they come after a nasal consonant or they are word-initial; this /b/ is also spelled as the letter "v", which I tend to pronounce /v/. 

Also, the /d/ is different from English - it's a laminal denti-alveolar (Wikipedia) and this is how it's explained on StudySpanish.com: "The Spanish "d" has two separate sounds, hard and soft. At the beginning of a word and after "n" or "l", the hard Spanish "d" closely resembles the "d" in the word "dog." The difference is that when pronouncing the hard Spanish "d", the tongue touches the back of the front teeth (rather than the gum ridge, as in English). In other situations (particularly between vowels) the "d" is softer, closely resembling the "th" sound in the word "this."" I think this is a pretty helpful description, and it's next on my list to practice!