Rome was not built in a day. We're an infant democracy. Take achievable walking steps before learning to run.
1. Get enough oppo MPs in to form 1/3 of parliament, to prevent PAP from getting a 2/3 supermajority vote to change the constitution at will to cement its hegemony
2. Then aim for the 51% mark to form a coalition oppo govt
3. Finally, a big enough oppo party or alliance to contest head to head with the PAP every election.