It's easy to begin growing houseplants if you follow these tips.
Start small. You can pick up many small plants at low prices. Your main investment is your time.
Know your house. The reason we even have houseplants is that they're suited for growing indoors. They come from tropical and subtropical areas around the globe and--most importantly--they evolved in shade. That's why they adapt to the lower light levels in our homes.
Understand that the humidity in most of our houses and offices is low. Most houseplants will thrive if grown in more humid conditions. Group them together and place gravel in their saucers. When you water, the excess water will pool in the gravel. As it evaporates, the plants experience a higher level of humidity.
Plants with high humidity needs can also be grown under glass. A cloche is a glass dome that covers a plant. A miniature conservatory is also an ideal structure to grow and display a collection.
Repot your plants as they grow. Move them into bigger pots gradually. If you put a small plant in a big pot, it will sit in wet soil and rot.
Water correctly. A good rule of thumb is to keep the soil just slightly moist, never soggy. If you get fungus gnats, you are watering way too much. It's fine to let the soil dry out moderately between waterings.
If you're having trouble figuring out when to water, get a moisture meter. It costs less than $10 and will save your plants from drought or drowning.