To see whether a teapot is good or not, one of the many indicators is flipping the teapot over and see whether the mouth of the sprout, the opening on the body and the handle are at the same height, thus the teapot should be able to stand firmly on the table upside down. However, this rule does not apply on some teapot shapes that are unusual. It applies to most conventional shapes though.
When glazing, try waxing the rim and inside lip of the lid with hot wax with some 100 mesh calcined alumina in it. This will stop the lid and pot sticking together (provided of course you fire them together!) and make for an easy release of the lid after firing.
If you have trouble with glaze blocking up your strainer holes you can cut up a piece of sponge and stick it into the spout, butting up against the strainer. This will prevent glaze flowing through the holes. An alternative is to pour out the glaze through the spout, which also prevents the strainer holes from blocking.