Altars depend on what you are going to use them for. Some altars are used for religious activities, while others are simply used for visualization and/or a place to hold ritual tools.
What do you intend on using this altar for? Your purpose might give other members a better way to help you set up your altar.
As for plant to keep in the home, you can't go wrong with flowers. They add a nice energy and feel to the place. As for herbs, I'd keep lavender, sage, mint, and parsley. Again if you could be more specific on what things you are wanting from these plants, we could help you more.
I am wanting plants that help bring calming energy into the home. I work a very stressful job and sometimes when I get home I find it hard to relax. I am would like to fill my home with plants that can help with this.
I love lavender and try always to have the scent around me.
I've always found aloe very calming, as well as lavender, gardenia, and other similar smelling/acting plants. Nice smelling plants tend to be relaxing, as does any sort of routine care for plants. This can give you the ability to meditate while moving and relax out your stress. It's why a lot of people love to garden. ;)
if you googgle search Images for altars, pagan altars, magick altars etc
you can view other persons altars and see what other have placed on their altars, some people also change their altars according to seasons, wheel of the year and/or whatever they are doing with the altar
I myself find it interesting to see other peoples altars
some of the magick forums online have threads posting pictures/photos of altars
amazon.com/ has some books on altars
To complete the altar following things are very important: - pentacle,wand,athame,bell,caudron,chalice,candle and censer...In short all the things you will use in craft work like casting spells mean you can put any other things you will use for your craft work or that mean something to you Blessed Be