When you are planting a bulb, the general rule would be to plant it about twice the depth of the bulb itself. Because some bulbs are much smaller than others, follow the instructions provided with the bulbs to decide if there is enough soil over top to protect them over the winter.
The ideal place to plant your bulbs is in an area that gets lots of sunlight and in an area that is well-drained. Also, be sure not to plant your bulbs where you intend to shovel or plow your snow.
A great option for fertilizer is bone meal. When planting the bulbs, mix some bone meal in the soil below the bulb because it will really help to develop the roots, and also because if it is too close to the surface it may attract animals.
Squirrels tend to dig up the bulbs. One way to combat that is to lay a bit of chicken wire on top of the bulbs before you back fill the hole. Another suggestion would be to lay some blood meal on top of the soil to discourage them. For people who live where deer are an issue, deer resistant bulbs such as daffodils or hyacinths can be planted to avoid this problem.
It is better to place several bulbs in one grouping because it makes more of an impression than just a single row. Odd numbers tend to look better than even numbers. Bulbs should be spaced out enough so that they are not touching. This is especially important because if one bulb was damaged or developed a disease, it won’t affect the others.