Even though Im a noob( I started sim racing like a week ago), I can tell you, F1 2013 difficulty is not that hard at all.Apart from playing with the formula cars in Gran Turismo 3, I had no experience with racing formula cars at all and even though Im still getting used to driving with a wheel and pedals, I 've had no problem getting better and better each race.Mind you I like a challenge, so from the start I went straight to Legend AI and no assists and racing only the circuits I know best.
Before each race I do a free practice of at least 5 laps, then before each GP (25% of the race for now) I do the full qualifying, which adds a lot to the immersion by the way and gets you pumped up and ready to race.If you do good on the qualifying and are starting at least 6th on the grid, if you are aggressive enough you can overtake 2 or 3 cars on the first corner, maybe more, add KERS and Rich mixture for the opening laps and you can snatch the lead and try to keep it from there.
The first races I started I did poor on qualifying, starting 15th+ on the grid and because I was still getting used to the game/wheel setup, I usually ended up losing quite a few positions in the first corners(AI doesnt help with the stupid rear ending) but still I tried to do my best to finish the race even if it was at last place.With more practice I make less errors and stay competitive for the majority of the race and have been finishing closer and closer to that podium, yesterday was my best, at SPA , I did lead the race until pit stops but , becauase of the stops I ended up 5th on the next lap, but I snatched the 4th place by the final lap, which felt great.
Conclusion: if you practice enough you'll find that gap getting shorter and shorter and if you get within that 1 second gap, DRS will do the rest to get you ahead.