For beginners to Otome games
PSP:
1) Wand of Fortune (otomate) - Is kind of lighthearted and Lulu, the main character, can be very likeable. Set in a western magic school, like hogwarts! I recommend using a guide for this one.
2) Kami naru kimi to - Is also relatively lighthearted with a very likeable main character.
3) Clock Zero (Otomate) - A very long but interesting story, I enjoyed it a lot. Might be a bit heavy or serious for some.
PC:
1) Ken ga Kimi (Rejet) - Set in Edo Japan. Story is relatively heavy and long, but there is a very good happy ending for every character. All the characters are well written and has a sense of reality to them. The development of their relationships is also at a good pace and is well written. The art? Gorgeous. Your japanese have to be pretty good, though. Preferably read up briefly on Japanese history first.
2) Ayakashi gohan - I'm still halfway so I cannot give a full opinion, but the characters are rich and the heroine is voiced, which is a plus for me. Has a long common route, which some may dislike.
Quin Rose has some really good heroines with interesting personalities, and I find that good heroines make me enjoy the stories.
Rejet has some darker, more serious stories in general, has more volume which I like.
Otomate can be a hit and miss, so I suggest reading up on the characters or review before playing. Diabolic lovers, for example, can be either well liked or disliked due to its special characters. (The art is beautiful though.) If you are fluent in english, I recommend breadmasterlee's reviews. I find them fun to read and informative. She does have the habit of not liking long stories though.
Advice in general:
Take note of the setting. School life, modern setting, and western magic settings are fine to get into straight away. They are usually more light hearted and suitable for all. You do not really need much prior knowledge to help enjoy story.
Historic otome games like Hakuoki or ken ga kimi can be a little difficult to understand due to the culture difference back then, and the different names for things. I recommend reading up a little about their time periods before starting, to help understand setting. Not necessary, but it does help. These can be quite heavy so caution there.
R-18 otome games can be good or bad. There seems to be a trend of...er...rape...so be sure to read a review just in case.
I like defined heroines, but your own tastes may be different, and if so you could try games like Amnesia.
Know that you do not have to see bad ends, and the skip button is free for you to use, or to just run on auto if you wish, for a character you dislike. Forcing yourself through anything never really make it enjoyable. Having fun is the point to a game, after all.
Reviews and walkthroughs definitely helps! There seems to be a lot of those on this forum, so they are available if needed.
Have fun!