It really depends on why I'm making the sim
If I'm running a pack test or other short term save, I'll generally start as the game intended - young adult sim, 20k simoleans, no skills.
If I'm starting what I plan to be a longer, more invovled legacy, I'll give my starting young adult sims what I like to call the "high school bundle" of skills - Charisma, Logic, Programming, Writing, Painting and Photography all at 2, and if it suits them, Acting, Archeology, and Selvadoradan Culture. These are the skills that your sims will develop if you have High School Years and actively attend every day for all 15 days your sim teen would be going to school, though I think only Charisma, Logic, and Writing actually reach 2 if you don't work on them otherwise. Without mods, I can't seem to cheat on a skill at level 1.
If I'm expanding family of either my own starter sim or an existing sim, I'll give them whatever skills, aspirations, and resources feel "right" for the storyline.
For premade sims, I usually don't change too much, as I only play with them if they end up joining my household for some reason, but I do have a long list of planned adjustments for my planned starter save (a very long list.)
For sims born in game, I usually try not to modify them too much, but if they logically should have higher skills (such as an adult with several kids via Neighborhood Stories) I'll sometimes cheat those on.
