It is advisable to do your first kit according to instructions, so you know how it is suppose to taste, before messing about with it. On the other hand, if you want to get better beer I would suggest:
(1) Destroy the instructions. Fire, shredder, it doesn't matter. You can be as creative as you like with this step.
(2) Clean and sanitise everything you will need: a fermentation vessel (fv), a large spoon or paddle, a small cup/glass, thermometer, a tin opener, hydrometer. You might need to rinse these things depending on which sanitiser you use. Probably best to sanitise a clean work surface too, so you have somewhere to put these things for when you need them.
(3) Fill the glass with about 200ml of water and heat in microwave for a few secs to get it to around 22C , sprinkle the packet of yeast from the kit on top, and give it a little shake. Keep shaking it every once in a while.
(4) Put a few litres of cold water into a sanitised fermentation vessel, and stir in 1kg of light or extra-light dry malt extract (DME), using your spoon/paddle. Or, alternatively, 1kg of brew enhancer (BE). DME is better though. Both BE and DME clump and get super sticky when dissolving, but it is easier to mix into cold water. Pour the stuff in slowly and keep stirring while you do it and it will be fine.
(5) Put the kettle on. Open the can from the kit and pour it in. Then, fill the can with boiling water from the kettle to dissolve the stuff that has stuck to the sides. With a towel or oven mitts, pour some into the fv, give the can a swirl, then pour some more. Just make sure that everything is dissolved and ends up in the fv.
(6) Using a mix of hot kettle water and cold water (tap is ok if your water tastes good, otherwise cheap supermarket bottled water is fine), start filling the fv to 20 litres. You want to balance these so that the final temperature is about 19C. Now take a hydrometer reading - you can either put the hydrometer straight into the fv (if so, remember to take it out) or use a sample tube (filled with a sanitised ladle, not dipped in the fv). I'd recommend the latter, as then you can drink the sample after taking the reading and find out what unfermented wort tastes like. When taking the reading, give the hydrometer a little spin first, and it might be worth taking a photo as its often easier to measure from zooming in to a photo then standing squinty-eyed trying to figure out where the meniscus is.
(7) Beat the living daylight out of your wort with your spoon/paddle. Splash it around, get some air into it, make it foam up. Getting oxygen in now will make your yeast happy. To be honest, skipping this step probably won't make much of a difference as this is a pretty low abv beer and the yeast will get an easy ride, but it is good practice.
(8) Swirl the yeasty water and chuck it in, put the lid on and leave the fv somewhere 18-20C. If your fv doesn't have an airlock, just crack the lid a bit on one side so the CO2 can escape. Otherwise, fit the airlock.
(9) Leave it alone for two weeks. Try to avoid large temperature fluctuations. Don't open the lid, mess around with it, take hydrometer readings. Just leave it alone. OK, ok, I know. This is your first brew. Just try to peek the absolute minimum that your curiosity will permit. If the airlock doesn't bubble, it doesn't matter.
After the two weeks take a hydrometer reading. It should be more or less around 1.008, or 1.006, 1.005, possibly even 1.010. If it is above 1.013 or so I'd be worried that it might be stuck, but it shouldn't be stuck as my understanding of the Wilko yeast is that it is pretty good. Now you can stick your two hydrometer readings into an online abv calculator and figure out how strong your beer it. It is now time to bottle. How you do this depends on whether your bottles are plastic or glass, what sanitiser you have, whether you will sypon from the fv, or have a bottling bucket with a tap. Either way, yeah, about 130g sugar is good for 20L of beer with a decent level of carbonation that is suitable for this type of beer. Once bottled, keep somewhere warmish (18-22C) for a fortnight, then somewhere coolish for a fortnight, then enjoy your must-better-than-what-following-the-instructions-would've-given-you beer.
