In Roto you have to have a more balanced team. In H2H you can get away with punting a category if you're dominant in the others (for instance saves or steals). If you do that in Roto it will kill you, because you're just giving points away.
Also, since you're measured on your entire season of work, there are guys who will really drag you down. Guys like Dunn and Sexson will just kill your average, so I would stay away from them unless you land a very high average guy earlier (like Pujols, Ichiro, etc).
Other things to keep in mind is that there is usually an IP and games played limit in Roto, so don't burn up all your games/innings early. Go ahead and sit a player with a bad matchup, when you wouldn't do that in H2H.
Last year someone in one of my leagues would put Hinske in at 1B when their regular 1B had an off day (Ortiz). They did this with the Util position too, and therefore couldn't play Ortiz the last 10 days of the season. The same person also burned up all their innings before September even hit, so they had a big lead in Ws and Ks and then watched helplessly as half the league passed them up as the season finished up.
The final thing I'll say is that with the structure of Roto I carry more hitters on my bench than I would in a H2H league. If I can have a backup at every IF position and the OF (multi-position eligibility is big here, guys like Hillenbrand or Huff or Ellis...), then you can make up for days when your starters have the day off. You want to maximize your stats, so don't leave games played on the table.
I prefer roto because I think it's a better measure of who really and truly has the best team. There's a lot less luck involved than there is in H2H. Good luck.