+1 interval training before nutrition. I have relatively good interval type athletic performance, but it is really extremely valuable for table tennis (FAST footwork response - probably even much more so than the other sports mentioned here) so it is a focus that I have become very keen to improve.
Also +1 don't drink too much water. You can give yourself lots of problems like acute hyponatremia (sodium deficiency) this way, even though you may have plenty of sodium in your diet and in your body. Solving this problem by ingesting lots of really salty food then leads to mild longer term hypernatremia (too much sodium), which will cause you to carry excess useless water weight, just to dilute the sodium and keep your body healthy (your thirst and water retention mechanisms will do this for you without much/any conscious intervention).
Some nutritional factors I have looked into that MIGHT be in play (probably some are, to some extent, but not necessarily all in any given case - I try to look after must of these just to be on the safe side, but it may be overkill for you. There could, of course, be other things as well):
- Glucose: sounds silly to even mention in a sports nutrition forum/thread but just in case you're not on top of it - you NEED glycogenation of your muscles, which ultimately comes from something breaking down to glucose. Simple/simpler carbs (sugars) do this more readily at lower metabolic cost. If you are mainly consuming high fructose/levulose "health" foods like apple juice, agave or honey (I'll guess no honey, since this is a vegan forum), you may be shooting yourself in the foot. While fructose is an isomer of glucose, it goes through a different metabolic pathway, and is usable only in much smaller amounts, together with glucose, to boost sugar uptake. Sucrose (cane sugar and in fact a good proportion of the sugar in most fruit), is easily broken town to 50% glucose, 50% fructose (a non-optimal mix but a good cheap base/starting point). SOME cheap maple syrup substitutes are essentially glucose syrup (check the ingredients - it might say something like glucose from wheat - what you don't want to see is "high fructose corn syrup" or "HFCS"). You can buy glucose supplements if you prefer. If you want something slower releasing (probably a very good idea) maltose (glucose+glucose disaccharide) is ideal. Traditional barley malt extract or rice malt syrup should be available in your supermarket. Both contain have some other useful minerals as well. Some fruits like bananas (many tropical fruits) also have more glucose than fructose.
- Magnesium: Deficiency is very common (especially in non-vegans but in many vegans also). Many athletic coaches and trainers believe it's really critical for performance and you can find it prominently in almost any mainstream pharmacist as a proposed solution to muscle tension, cramps and joint aches. You could take the supplements but it's actually pretty easy to get it into your diet. Seaweed is a really rich source. Cacao, coconut water, many nuts and (dark) green veges if they're grown in good soil are all contributors as well. I would suggest eating a bit of seaweed even twice a day (I usually eat 5-10 meals, though). So many different ways to eat it, and lots of other nutritional advantages too.
- B vitamins, especially B3 (niacin, also called nicotinamde or nicotinic acid): is critical for human energy production and hormonal regulation, also DNA protective. Some athletes deliberately supplement to way over the RDI but obviously there is an extent where medical advice is probably advisable. There is some in lots of foods (e.g. capsicums, tomatoes, green peas and beans) but if you're concerned about this, try eating more shitake mushrooms or asparagus (rich vegan sources) or take a supplement. Some foods are also fortified with it, as are No-doz plus caffeine pills (not the regular no-doz, which are just caffeine). Nutritional yeast fortified with B vitamin complex could be a good solution. Tryptophan (amino acid) is apparently also a co-factor for B3 but I doubt it's an issue if you're getting plenty of protein, unless it's all from hemp.
- Creatine: Yes, really, it works (for a specific purpose: this one). There's lots of research about it, not very equivocal. I'm sure, and so are a lot of people who are far more knowledgeable than me like the folks at the Australian Institute of Sport. Non-responder groups in one or two studies are probably mainly or entirely converted to responders simply by taking it with sugar after training (the insulin spike drives absorption).
- Coenzyme Q10: more likely at issue if you are older or middle aged. I am not, but I look after it anyway, because it's easy. 3 vegan foods (maybe others) are quite rich in this: soybean oil, grapeseed oil, red palm fruit oil. The last has lots of quite good nutritional benefits while the first seems to me like an especially bad idea. Why not get a bit of red palm oil anyway? It's great for cooking, usually quite sustainably produced, absolutely LOADED with vitamins, carotenes and antioxidants, and a moderate dose of medium chain saturated fats will probably do you more good than harm.
- Carnitine: non-essential nutrient but could have a marginal impact. You can get some from miso or tempeh, or possibly find a vegan L-carnitine supplement (I have no idea whether carnitine supplements are normally vegan, I guess most likely so, but you'd need to check). As you can tell, I don't bother with this as a supplement.
- Taurine (as with creatine and carnitine, our bodies synthesize quite enough for health but maybe slightly less than optimal for short response athletic performance). Unfortunately it is not available from any vegan foods, but the supplements are vegan, because it is cheaper to make that way. So go ahead and have an energy drink with some taurine, or try a taurine supplement. With the energy drinks, beware that with some brands such as Monster, other trace ingredients are actually produced from dairy. You can find the fine print on the can or do a little research.