Writing Forum

I really need advice and guidance. I am a member, but I haven't been here for quite a while. I tried the genre once and more or less got lost. My interest in Sci-fi and Fantasy has grown, again. I started on an idea that I think may be a cross between the two, but to date it is full of holes. Can anyone give me advice on how to get a strong start, type of character profile to use and just any advice about writing in that genre?
Thank you,

Kristina