RE crude spreads,I have made a living trading commodity spreads.
The most important relationship is the stocks in a deliverable position vs. the size of the open interest of the nearby. If physical stocks are sufficient to cover the nearby month there is less chance of a participant standing for delivery and squeezing the market. The market will then be less willing to pay a premium for the nearby relative to the deffered and the spread will gravitate
towards full carry.
The composition of the open interest is also important and plays a role. Where the long in the nearby is a spec position, index funds for example, the market is less concerned about a potential squeeze as specs do not typically take delivery. Again, the spread should gravitate towards full carry.
The specifications of the contracts also influence spreads. Where there are position limits for the delivery months, this may be a disincentive to take deivery if the limits are sufficiently small. This example favors the short and can be a perpetual characteristic of the contract. I have used this stategy to trade against funds for a number of years.
Personally, I would not use technicals to trade spreads.
Hope this has been of some help.