The method you use to get to Lavos is largely irrelevant, although it can introduce minor variants in some endings. The first method to reach Lavos is via the right telepod at the Millenial Fair, where the sparkle is. You can also reach him via the bucket at the End of Time, by crashing the Epoch into him (set the time period to 1999AD - Day of Lavos), or by proceeding through the Black Omen at the end of the game.
The final form of Lavos is fairly powerful; the left orb is immune to magical attacks but only has 2000HP; the right orb is the orb you want to defeat, but is defended from all attacks unless it is reviving one of the other two components; this orb, Active Life, has 30,000HP. The humanoid center has only 10,000HP, but also has the most powerful attacks. The center can use Crying Heavens/Hidden Blow at any time, which is devastating on a weak character. The other attacks are dependent on the time period (remember that Time Warp at the beginning of the battle?):