With this question it is important in your introduction to start with your principal argument , eg 'the south sea bubble crisis was very important in Walpole's rise to power because..' and then list your 3-4 main argumentative points. Once you have explained your argument, it may be useful to mention the opposing points eg 'Of course, there were other reasons for Walpole's ascendancy, such as..., however these are merely peripheral factors to the critical event of the south sea bubble crisis'. The intro is all about providing your argument, as this will form the basis of you essay structure and tone. It is best for first 2-3 paragraphs to consist of your argument, and in this case in your first paragraph it will be useful to define what the south sea bubble is (this can be done at the start of your intro if preferred) eg 'the south sea bubble crisis exploded in 1720, with the huge fall in stock prices of the South Sea company. This triggered public outrage as it exposed the corruption within Parliament by those who had been influenced to take payments in return for supporting parliamentary bills that benefited the company'. From here you can explain how Walpole manipulated the situation. For an argument supporting the hypothesis of the South Sea crisis helping Walpole's rise to power, argumentative points could include his handling of the finances (evidence would be his convincing of the Bank of England and East India company to take over £9 million of its stock to stop the free fall in its value), how Walpole saved some key ministers such as Stanhope and Sunderland, how his handling neutralised public outcry (e.g him turning public attention away from the crisis by exploiting the Atterbury plot), how it restored strength to the Hanoverian regime and the significance of his being appointed First Lord Treasury in 1721.
Within your paragraphs it is key to explain your point, provide evidence, explain the evidence and link it back to the question - try to mention terms from the question in every paragraph as this shows that you are engaging with it. Within a timed essay, it is also important that you don't get too bogged down in detail, and avoid narration - paragraphs don't need to be a page long in order to convey analysis, and don't be afraid to have a clear opinions. It can help to structure your essay if you know exactly which side you fall, and language that suggests you're on the fence can often come across as you not actually knowing how to analyse and use evidence. Balance is key to essays, and thus you should include 1-2 paragraphs explaining the other factors that contributed to Walpole's rise to power, such as the weakness of the Tory party, his use of patronage and political alliances and his responses to the Jacobite plot of 1715 and 1722. It is important to also provide evidence with these points, but it may be useful when providing analysis to say something like 'the weaknesses of the Tory party were clear as they had been out of favour since the Hanoverian succession. George I's deep disdain for them and their supposed betrayal of Hanoverian policy at the treaty of Utrecht, and the Jacobite association they had gained from Walpole had contributed to their dire situation. However, even if the weaknesses of the Tory party opened the door for a Whig supremacy, this did not make Walpole's rise inevitable, and it was his own actions that allowed him to occupy the position of leader. The South Sea Bubble crisis was a critical moment in his political career and his actions in resolving it were more important in ensuring his success, rather than just the success of the Whig party'. This example ensures that you provide evidence and analyse why it does not do enough to undermine your argument. Finally the conclusion should just act as a more detailed summery of your argument, noting your points and the opposing theory - try not to repeat your intro through referencing greater detail that you discussed in your essay.