There are lots of easy ways without cheating to get LP. The easiest is to complete the goals they give you (like making two sims date or modifying a room), you will usually get 1 LP per goal. Also get your sims into hobbies, such as fashion designing. The reward for collecting the final sets of objects is 3 LP, and once you have collected all sets, you can choose to 'start a new collection' and get 3 LP again the next time you collect the final sets of obects.
The competition centre also gives out 3 LP as a first prize (1LP as a second), so try to make each sim have a maxed out hobby or career for you to enter them into.
It's also not too late to earn simoleons with CC (if you haven't got any CCs, quick, get your sims woodworking!). Buy a 60CC firepole then sell it for 150 000 simoleons, and you'll be a millionaire in no time.