When it comes to altars, people have ideas how it should and shouldn't be done. In reality, all they need to be is simple. Nothing truly fancy is needed, a statue, tablet or image/photo of the deity, buddha, bodhisattva or ancestor(s), two candles, an incense holder and if needed a vase with flowers and/or food. If you are making an altar, just remember that all that is needed is these basics which does keep it simple. If something is wanted to be added, it can always be done.
What I don't see a lot of people considering even if it would be helpful is the use of spirit tablets. If you cannot find a statue or image of a deity, buddha, bodhisattva or ancestors to use on the altar, using a spirit tablet instead is a good idea. All that is required is a small but thick block of wood to act as support and a thinner but longer block. Just write the name(s) of the deity, buddha, bodhisattva or ansestor(s) on the longer block and then glue it to the thicker piece.
For offerings, it is always good to light up two candles and light some incense. As I view it, this is truly all that is needed for offerings. It doesn't have to be but can be. Depending on whom is being worshipped or venerated it is always important to consider what is proper to offer and what is best to avoid offering. It can be flowers, water or some sort of easily gotten or prepared food. It doesn't always have to be such, as depending on whom is being worshipped or venerated it may be an idea to offer tobacco or some sort of alcohol. It is a matter of learning what is best to offer and what should be avoided offering.
As for altar placement, I have heard on a number of occasions that the bedroom is to be avoided at all cost. This isn't always the case. With some deities it is probably best to keep the altars to them out of the bedroom. But for many I have noticed that it doesn't matter, for two deities in particular it is actually best to put the altar for this husband and wife duo in the bedroom. They are Chuang Mu and Chuang Kong. These two deities are a pair whose duties involve the bedroom and what goes on in there, and as such their altars should be in the bedroom. It could be the same for other deities which I am simply unaware of.
The altar of some deities is best placed in a certain place of the house and should be considered, where altar placement for most deities seem to not matter that much. From personal experience, the bedroom is one of the best places to put an altar. It also comes down to the amount of space in the house and what can be done.