To improve your own personal language skills:
1. Use technology. Software, apps, games. The Rosetta Stone software, although expensive, works pretty well if you have the time to use it. The military kept up their contract for many years because it's so good.
2. High interest reading material. Pick up some magazines, in paper or on your device to practice words in categories that already have your interest perhaps cooking and housekeeping or cars or science.
3. Listen to music in the target language. The radio is a great place to hear authentic conversation on local topics of interest. Plenty of internet radio stations also are culture or language specific.
To improve and encourage the language skills of yourself and your child:
4. Listen to children's music in the target language in the car when you are driving around together. Sing and talk with your child while practicing simple or fun songs. Many libraries have children's books and CDs in many different languages.
5. Make it a routine to read one book in the dominant language and one book in the target language every day to your child. This can easily become part of your bedtime routine.
6. Use a picture dictionary for yourself. Have it available around the house and practice vocabulary with your child. Alternatively, use a translating or dictionary app to help you learn and practice new words in context.
7. Pick a certain experience that you engage in regularly with your child. Maybe a certain meal, during bath time, or an evening walk. Study up on some of the words that you imagine you'll need to try to sustain the minority language for the entire length of the experience.
8. Choose to allow screen time in the target language. Did you know that Sesame Street is in over 140 countries in several different languages? I have several episodes of Plaza Sésamo on my phone to help prevent restaurant or other public melt downs. I've heard some parents say that they just switch the language on favorite movies to allow their child to watch it in the target language.
Really, the goal is to surround yourself and your child with more opportunities to hear and practice speaking the target language. I even switched the settings on my phone to a different language to allow me yet another way to make me think and process in the target language.