This seems to be a recurring theme, and people that know me have suggested that I do a few more. So here we go with another half dozen of the problems you might come across.

Too sweet. Of course this assumes that you were not going for a sweet beer anyway, in which case no problem. Mind you, even a stout or other "sweet beer" can be too sweet, but you definitely don't want it in a bitter. There are two main causes of this, one is an excess of malt, where the remedy is to add half a teaspoon from your starter bottle to the fermenting vessel. The other is insufficient attenuation, that is where the specific gravity is below 1.010. Unfortunately there is no remedy for this, and if the brew is completely undrinkable (we all know someone who will) all you can do is discard it.

Too lively. A fairly common problem and relatively easy to fix. There are three main causes here. The excessive use of priming sugar, where you need to decant inro a large covered vessel, avoiding contamination. Too high a storage temperature. Just remove to the correct temperature of between 50-55F. And too high a specific gravity when bottled. Add half a teaspoon from the starter bottle, do not seal too tightly, and release the gas daily.

Yeast Bite. As the name suggests this is an excess of yeast, giving an intense acrid bitterness. An excess of yeast can be removed from the periphery of the fermentation vessel along with any waste matter by simply using a damp cloth. Any yeast still in suspension can be dealt with by adding more finings. Sometimes storing at too high a temperature will cause sediment to rise and disperse. Simply remove to the correct temperature of 50-55F.

Lack of a decent head. Four main causes for this condition. Using faulty malt. Nothing to be done here except throw it away and start again. Maturation time too short. Ah, the impatience of youth! Can be rescued by pouring into a large covered container, sparing use of the starter bottle, and moving to a slightly higher temperature. A lack of dextrins, which means the mash has not reached a temperature of a least 152F. You can try heating to that temperature. The simplest cause is using a drinking vessel that has not been washed and rinsed properly. Clean glasses are a must.

The beer tastes "off". This can be caused by the decomposition of dead yeast cells. Remove by racking.

Cloudy beer. A contentious one this, as some drinkers don't mind as long as the taste and flavour are OK. However the majority of beer drinkers like to see a nice clear product. Causes are storing at too high a temperature. Just move to somewhere cooler. Insufficient sievings of hops and grain malt. Adding finings will usually solve that. Excessive use of finings. Nothing to be done, either drink as is or discard. Too few finings. Add more, carefully. Filtering too soon or ineffectively. Filter again.

OK, there we have it. If you are thinking that there is just so much to go wrong it just isn't worth it. Don't be put off. You will usually produce a perfectly drinkable beer. It's just useful to know a few of the things that can go wrong, and how to fix them if possible. Of course, the likelyhood of things going wrong are drastically reduced if you find a good beer recipe, and stick to it. When you have become a reasonably competent brewer, then you can go and experiment.