Without looking at blueprints, all you can do is make an educated guess. Possible methods include:
If it's an exterior wall it's almost always load bearing.
If the joists are not continuous over the wall (they are cut short and meet on top of the wall) it is definitely load bearing.
If there is a load bearing wall or beam directly above or below this wall, it is likely load bearing.
Check the direction of the joists (as you mention). If a joist is running perpendicular to the wall, or happens to fall directly above/below the wall, it can be load bearing.
If there's a single top plate, the wall most likely isn't load bearing, unless the wall uses deeper studs than 2x4 (such as 2x6).
Expose the wall over a doorway or pass-through. If it's a solid 2x6 or greater turned vertically going from the jack stud on one side to the other, there's a good chance the wall is load bearing.
If there are only cripple studs on a flat 2x4 to give you something to attach the drywall, it likely isn't load bearing.
Look for signs that the wall was added after the house was built, newer wood materials, drywall or finished flooring that extend over/under the wall, etc. If the wall was added, then it isn't load bearing.
Calculate the span from the known load bearing walls on either side of the wall you are removing, look at the type, size, and spacing of joists above the wall, and calculate if the joists can support the load above the wall without the wall being in place. If the joists can't support the load without the wall, then by definition, it's load bearing.
When removing the wall, cut the studs with a sawzall. If the blade begins to bind in the middle of the stud, then there's load coming down from the ceiling through that wall and there's a good chance it was load bearing. Stop what you were doing and sister a stud to the one you were cutting.
If, after you remove the wall, your home collapses, it was load bearing.
If the wall is above a basement or open crawlspace, you can look from below to see if it is on a bean or above a support post. If it is not, it still does not mean it is not load bearing, but it can help to understand the structure.