After your spread is laid out you have the task of interpreting its meanings. This involves a mixture of logic and intuition.
First, look at the overall weight of the spread. If you have equal numbers of positive and negative cards, then each card's meaning should be taken at face value. If you have more positive cards than negative cards, you can assume the severity of the negative cards will be lessened. Conversely, more negative that positive cards weakens the positive cards in your spread.
Cards may also negate one another. As an example, a card that claims you will experience health problems can be negated by a card that claims you will enjoy good health.
It is important to remember the meanings of the cards are symbolic. Often you will have to interpret the card's symbolism within the context of its position in your spread. For instance, if you are using the Zodiac spread and have a card in the House of Taurus (Matters Concerning Finance) that speaks of death or illness, this is probably a warning that your finances are in jeopardy.
Of course we would all love to have all our spreads be overwhelmingly positive, but reality just doesn't work that way. So what do you do if you get a very negative spread? First most negative cards are warnings, so heed them. Secondly, while you may not have complete control over the events in your life, your will and ability to choose paths wisely do empower you to have great deal of influence over the direction your life takes. For instance, if you get a card that predicts poor health and you smoke, fight back by giving up smoking.
Finally, although rarely, regardless of how you view it, your spread may make no sense at all. If your spread seems way off base, just go back and get another one.
Ultimately, the value of your spread is directly related to how honest you are willing to be with yourself. The more honest you are the more you will gain from reading the cards.