If you want to create adult siblings but don't want the elder parents in the family, create the elders first, use Make a Child for each sibling, and delete the elders. The result is a group of Sims genetically created by same two Sims but with no actually existing parents.  Link them up by the Family Relationships tool and your ready to play.

Science:  Serious, Neat

Medical:  Serious, Neat

Business:  Serious or Playful, Outgoing

Criminal:  Active, Playful

Athletic:  Active, Outgoing

Culinary:  Serious or Playful

Law Enforcement:  Serious, Active, Neat

Military:  Active, Outgoing

Politics:  Serious or Playful, Outgoing

Slacker:  Outgoing, Playful

A Sim's astrological sign has nothing to do with his birthday, but is rather a reflection of his personality settings.  So twins may have different signs despite their identical birthdates.

Memory Markers can trigger jealousy. If a third party Sim witnesses another Sim cheating on his significant other, she gets a memory Marker for it. If, by chance, the third-party Sim talks about the Memory Marker with the cheating Sim's love, the cheated on Sim will react as if she witnessed the betrayal.

Babies:  3 days

Toddlers:  4 days

Children:  8 days

Teens:  15 days

Adults:  29 days

Elders:  9 to 31 days

Though if may feel odd, it's ok to leave babies on the floor. No one will step on them and it gives them a chance to take in the world around them.

Extremely Sloppy Sims are Bladder multi-taskers:  they use their shower time to satisfy Bladder as well (though it's slower than using the toilet).

The only other thing on which a Sims can relieve themselves is a shrub. This can be done only by very Outgoing and very Lazy Sims, and only when their Bladder Need is very low.

Sims can autonomously take a sponge bath in any sink but only if their Neat/Sloppy is below 6 and current Hygiene is less than -50.

If there are a lot of flies in a Sim's house, they can converge into a huge super swarm that can literally kill a teen, adult, or elder Sim.

Kids in private school with good grades get skill points as rewards (instead of money).

You can also hand a Sim-made painting on the wall. Paintings created by high Creativity Sims (4-10) appreciate in value.

When paintings are done, they have a Sell interaction. Use this to sell the painting, or you can "return" it in Buy mode as you would any other object. Keeping a painting is also an option because it will appreciate over time and be worth more in the future. For the very patient, waiting until the artist Sim dies dramatically ups the value of the painting. Stockpile a Sim's high-value paintings and sell them upon her death for a big dose of income.

Party guest maximums are dictated by your computer's processing and memory power. The slower the processor and lower the RAM, the fewer guests can attend.

Assign the Sim with the highest relationships to the largest number of Sims to make the invitation call. This increases the odds of having a well-attended party.

If no living Sims are on the lot when the Reaper comes to claim someone, there's a random chance he'll use the bathroom, make himself a drink at the bar, or watch a little TV before departing.

Pleasantview's most famous missing person is actually a Townie in Strangetown.

Keep in mind that Neat Sims with low Mood may have a Fear of using public toilets. Taking them to Community Lots, may pose challenges.

Success at darts is based on a Sim's Mechanical skill.

If an adult Sim uses the Farstar e3 Telescope between 7pm and 2am to Stargaze, there's a five percent chance that he'll be abducted by aliens.

While the Sim is gone, his Need meters fluctuate wildly. When he's returned three hours later, however, the Sim will be the same as when he left. Unless , of course, the Sim in question is an adult male, Anytime an adult male is abducted by aliens, he will always return pregnant.

Old Age:  White

Drowning:  Blue, leaves puddles behind

Electrocution:  Yellow, spark and electrify occasionally

Burned:  Red, smoking

Death by satellite:  Orange, (yep, while doing Watch Cloud (daytime) or Stargaze (nighttime, not with telescope) outdoors. very small random chance a satellite will fall and crush them. 

Death by Flies:  Purple

Disease:  Green

Scared to death:  Pink