How do I remember all the content? Okay so I agree, the A-Level Chemistry syllabus is huge and a massive nuisance. However, there are ways to make it easier. I've divided these based on the topic because I think each topic deserves its own special unit.
1. Physical Chemistry This seems to be the most 'manageable' in AS, but in A2, it's a whole other level of pain. The calculations are so intense and they make me want to cry. The only way to really tackle these is by solving as much as you can, there is no way you'd get this by memorising.
2. Inorganic Chemistry This on the other hand, is just memorisation in my opinion. Best way to memorise things? Active recall. Flashcards are great for this, and I have a deck for all A-Level Chemistry topics on Quizlet. Solving past papers will obviously help, but make sure you're able to easily recall details first.
3. Organic Chemistry This, is by far the biggest pain the buttocks I've ever encountered in any subject. However, I also enjoy it significantly more than the other types of chemistry in the syllabus.
How do you get to tolerating organic chemistry from where you are right now? Solve as much as you can, again. My teacher says organic chemistry is like puzzle, you really need to think to master it. Once you do, an A* is probably in really close reach of you. Best way to memorise the reactions again is using active recall (see above for Quizlet link) and also using flowcharts. Draw the reactant (e.g. phenol) and draw all the reactions with phenol you've observed from your notes / past papers. Stick these up on your wall where you study, it'll help with remembering them more easily too. Since the questions themselves are like a flowchart too, this helps.
4. Analytical Chemistry There are challenging parts of this too, so solve as much as you can again. Other elements, memorisation helps too. However, make sure you actually understand what you're memorising.
How do I prepare for paper 1 (multiple-choice)? This paper is simply awful and I hate it. That being said, prioritise this a lot, and SOLVE AS MUCH AS YOU CAN. That's all I have to say.
How do I prepare for paper 3 (practicals)? It's really easy to lose marks in practicals. Plus, the amount of papers you actually get to do in the lab is pretty limited too. Therefore, practice papers on your own with random values. Try doing the calculations with these values and make sure your steps are correct. The calculation part can get tricky and you'd end up stuck, so ensure you have enough practice with those.
Other aspects about the practical exam I'd like to discuss are - don't worry if you're not getting the correct result. If you know that your measurement is not right, manipulate the data. The data you collect is used to plot graphs and your graph might end up awfully wonky-looking if you have values that are significantly off. Therefore, memorise the general shape of endothermic and exothermic graphs and how to extrapolate them beforehand.
Next, do all your calculations before moving to qualitative analysis. If you get stuck in qualitative analysis, it might take forever getting those answers so make sure everything else is done before that.
Lastly, regarding titrations. You already know your titres have to be within 0.1 cm³ of each other and if you feel like you don't have time to carry out a lot of them, just manipulate the data again.