Supporting a proposal successfully isn't a one click and forget it kind of deal. There are several different phases that occur during the proposal period-what is required of us in each stage is different.
To support Joomla in the definition phase, we need to follow the proposal, need to ask good example questions and vote on the ones we think are suitable for a Joomla QnA. Comments about how to make questions better or why they are bad are important for making better quality questions through edits or writing new questions.
In the commitment phase, we need to reconfirm our support for the proposal. You might think that showing support during the definition stage automatically means you support the commitment phase, but this isn't the case. An interesting thing to note about this stage is that if you have rep of over 200 on any other StackExchange sites then your commitment is worth more. Each site with rep over 200 helps. Note that once you reach 200 points on any StackExchange site you are automatically given 100 points on every StackExchange site that you sign up to (or have already signed up to).
Next step is the Beta stage. Not all proposals make it this far.
UPDATE: The below image was taken from another proposal that had completed its Beta stage. It is a good example of what is expected of us during the Beta stage.
The 3 stages need to be completed in less than 2 years otherwise the proposal will be closed down(again).
How can we further support Joomla?
Finally, if you want to show even more support for the proposal I recommend mentioning a link in your profile, making a chat channel in Stackoverflow or just telling people about the proposal when appropriate. For the die hard supporters, it might be possible to take out advertising either on StackExchange or Google Adwords or something like that. If you have any other ideas I would love to hear of them!
IMPORTANT UPDATE REGARDING COMMITMENT STAGE
According to https://meta.stackoverflow.com/questions/53650/area-51-commit-percent/53733#53733 our commitment score will decay over time. To prevent this, we must keep visiting the proposal (while logged in) to refresh our vote.