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Writing novels takes practice too, just like drawing.
Literal
Novels [even-だって] pictures [same-as-と同様に] practice [subject-が] is-necessary [explanatory-なんだから].
だって here is the emphatic 'even X' — 'even novels (not just art).' と同様に ('in the same way as / just like') draws a parallel to drawing. なんだから (= のだから) adds an explanatory, slightly insistent tone — the speaker is reminding or arguing a point, not just stating a fact. The whole sentence has a persuasive, slightly exasperated register, as though pushing back against someone who thinks writing doesn't require practice.