Hoyas, commonly called waxplants, are native to (predominantly southeast) Asia. Most varieties are lower-maintenance plants that can be grown successfully in the home in temperate climates. Estimates of the number of hoya species range from a few hundred to over a thousand, with most estimates falling in the sub-500 range; my collection includes hundreds of different hoyas, including a few dozen hybrids and cultivars. Hoyas are collected for both their diverse, usually-succulent foliage, as well as for their flowers, which form in clusters called umbels.
Most hoya species grow best in very bright, indirect light, but some species can tolerate at least some direct light. A number of species display interesting changes in the color of their foliage when grown in brighter conditions. The two most sought-after changes are colloquially called sun-stressing and splash.
Sun-stressing: Sun-stressing refers to a variety of protective pigments that plants make to protect themselves from absorbing too much light. Many hoyas will slowly change from deep green to a palette of sunset shades as light levels increase; this includes the aptly-named Hoya "Sunrise," as well as Hoya obscura. A smaller set of hoyas will take on pigments that are darker in color, often a deep purple or near-black tint. Some cultivars of Hoya lacunosa (or maybe krohniana - I've not seen the species consistently identified) will become almost black in bright light.
Splash: "Splash" refers to silver-to-pink flecks or sections that appear on leaves under certain conditions. Splash is not caused by pigments like sun-stressing; it's actually the result of air pockets in the leaf reflecting back light. I find that my splashiest hoyas get bright, indirect light, but I do have a few that keep the trait even in moderate amounts of direct light. Most "splashy" hoyas display this trait due to environmental conditions. With the exception of a very few (often very expensive) cultivars, you should save your money and purchase a "plain" hoya of the same species. Splash is largely triggered by light levels, so give your plant bright, indirect light for a few months, and you should see some splashy leaves!
In my growing experience, hoyas will almost never be splashy and sun-stressed at the same time. A plant that is getting yellow or red leaves from sun-stressing is almost always in far too much direct light to promote splash.
Additionally, many hoyas do not develop attractive sun-stressing or splash when in bright light. They will simply look chlorotic or even burn. If you're not sure what category your hoya falls into, just increase the light slowly over a period of 1-2 weeks and keep an eye out for sun burn.
Personally, I grow most of my hoyas about 1-15 feet back from a west-facing window, purely because that's the space I have available! I keep the blind wide open, and just place the plants that want less light at the far end of the shelves or behind another plant.
Water your hoyas. There is a myth floating around the internet that hoyas should be bone dry between waterings, or that you should wait for the plant to show signs of wilt (flimsy or dropping leaves) prior to watering. Do not follow this advice unless you are a chronic overwater and truly cannot control yourself any other way. Wilt is not a sign of a healthy plant. If the plant is wilting due to dryness, you needed to water it yesterday.
Many hoyas are very drought-tolerant. (Some hoyas are not - your thin-leaved hoyas won't survive long with bone-dry soil.) Generally, the more succulent (fleshy) a plant's leaf is, the more it can tolerant spats of time without water. However, being drought-tolerant doesn't mean that your plant will grow well (or at all) while being deprived of water.
Water your hoya when the soil around the roots is dry or nearly dry. If your plant's roots fill out a pot, that means you need to check the soil all the way down near the roots at the bottom of the pot, which will often stay wet longer than the soil on the top. If your plant is a freshly rooted cutting and only sitting in the top third of your pot, don't want to water it until every speck of soil is dry! What matters is the moisture around the roots, what the plant is actually able to access. Water your plants thoroughly, letting water drip through the bottom of the pot.
You can determine how moist the soil is by using your finger, a moisture meter, or by gauging the change in weight of the plant pot. Watering by weight is by far the fastest and least messy method, but you'll need to use your finger or a tool for most large pots or plants in medium you're not (yet!) used to. A reliable moisture meter can help you get better at this estimation.
Most hoyas will have prominent venation, be somewhat shiny, and feel plump when appropriately watered. You'll know it when you see it!
I won't provide any guidance on how often you should expect to water, because there's too many variables that can impact this frequency. But I suggest that you check whether your hoyas need to be watered once or twice a week until you learn the frequency required in your conditions, and take these factors into consideration:
Succulence: Plants that are fleshier tend to be tolerant of dry spells - though that doesn't mean the prefer them!
Rootbound: A rootbound plant is going to require much more frequent watering than a plant that is freshly repotted into a pot of an appropriate size.
Humidity: Plants in higher humidity environments will lose less water through their leaves, and therefore have lower moisture needs and take up water more slowly from the soil. A plant that is in a room dried out by central heating in the winter can eat through water at an alarming pace!
Maturity: Very young plants with immature roots will not tolerate a lack of water as well as older plants can. Try to minimize or eliminate the amount of time newly rooted spend in completely dry medium.
Pot: Plants in terra cotta or net pots will dry out much faster than plants in solid plastic pots.
Hoyas are happiest at warm room temperatures (in the 70s). Many are hardy down to the 50s, and some can survive sustained temperatures in the 90s, so growers in certain areas can keep their plants outside at least part of the year. For a new grower, I'd really suggest keeping them inside so you have more control over the environment and can better learn your plant's needs.
Hoyas need well-draining medium. Unless you purchased your plant from a specialty hoya nursery, the soil your plant came in is almost certainly not a suitable medium. Hoyas are somewhat epiphytic plants, so they do well in mixtures that incorporate a good bit of orchid bark. I've had success with Doug Chamberlain's soil mixture. I also have hoyas in pure orchid bark, which works fine aside from needing more frequent watering for good growth.
A good rule of thumb is to start with one-third each of perlite, orchid bark, and potting soil, and adjust from there based on what you learn about a particular hoya's needs. You can substitute here - I like coco coir as a soilless alternative to potting soil. You can throw in some horticultural charcoal or crushed oyster shell, but these addendums are definitely not necessary.
Indoor plants without true dormancy periods can be fed year-round. I prefer to feed every time I water - which in practice translates to whenever I remember - with a fertilizer that I can directly add to my watering can.