Of course, you could write to the bishop. But the bishop will probably only intervene if things are very bad indeed. And even then he doesn't have much power, if the priest is intransigent. So what can one do? I can't speak from experience, but I can share what I've mentioned above - that I've heard good things about what happens if people take some initiative.
There are two things that are important, it seems. The first, unsurprisingly, is prayer. Pray for the priest, for the parish, for whatever or whoever seems to be the problem (not forgetting, of course, to pray for yourself, knowing what a problem you are). But to be effective, the prayer has to be communal - a group of the faithful must get together to pray, and perhaps also to fast. I have heard of converted clergy resulting from this. In one striking case, however, when a community of sisters started to fast and pray for their parish priest, he was dead within the week!
The second important aspect is summed up in the well-known phrase, 'Be the change you wish to see'. Again, the 'you' in this case is plural. If your priest is teaching heresy, get together to study the Bible and/or the Catechism, or other worthy material. If he's dull and uninspiring, get together to share and do things that inspire you. If he's uncaring, form a group to provide help and care to those in the parish community who've been neglected. If the liturgy's as dull as ditchwater, then meet together to praise God in more enjoyable ways. You don't need the priest's permission to do these things if you meet in your homes or at non-parish venues.
All of the above assumes the priest is the major problem; but as I said at the beginning, he may be fine and the parish be the problem. In which case you (plural 'you' again) can form for the priest the nucleus of a new community.
Most success, it seems, is to be had if the group of loyal disciples aims to be evangelistic. Only thus does it impact on the wider parish. Moreover, if you're going to evangelise, that necessarily means you have to put all the other elements in place: prayer, community, teaching, and care. Once new members start to come into the parish as a result, this inspires and re-energises the whole community, including the priest – although the process is not without its challenges, of course.