When I use Manipulate I can do:
Manipulate[x, {u, 1, 10}]
In reality my controls are many and complicated, so I would prefer to take their defi
Manipulate has the HoldAll attribute. You can force control to evaluate and everything works ok
control = {u, 1, 10};
Manipulate[x[u], Evaluate[control]]
The problem with this is that the variable u is not properly localised, so if you have already set, e.g., u=1 somewhere, then the Manipulate will return an error.
It might be better if you use appropriate scoping constructs such as With or DynamicModule depending on exactly what you're trying to do.
This is maybe overkill, but it ensures that u is local and moves control outside of the manipulate:
DynamicModule[{u}, With[{control = {u, 1, 10}}, Manipulate[x[u], control]]]