A certain amount of yellow leaves on an Indoor Bonsai are completely normal, leaves on an evergreen tend to last about 3 months, then drop off and are replaced by new ones, about once a week or so go over your tree and remove any yellow leaves.
In the summer fill a bowl with water at room temperature, deep enough to cover all of the soil in the pot. In the winter lightly top water your tree by pouring water over the soil when it feels really dry as they do not use as much water during the winter months. Water when the soil feels really dry and not before.
Your tree needs plenty of light (i.e. the brightest window you have). Without enough light growth will be leggy. Any warm bright area will do, if there is only one light source, i.e. one window, turn your tree round once a week to get even growth. When you find a place your tree likes leave it there, you will know it’s happy because it will grow many new shoots and flourish.
Your tree needs pruning all year round, more so in the summer months. Cut off new shoots once they grow to about 3-4 inches long, prune between a
Brown Crisp Leaves: Lack of water, follow watering instructions above.
Every Leaf Turning Yellow: Over Watering, as above.
Glossy, Sticky Leaves: Your tree may have Aphids, such as Whitefly or Greenfly, check under leaves for both insects and eggs. Use mild insecticide, spray under the leaves about every 3 days, this should encourage them to leave.