If you've done wet lay then mould making shouldn't be a problem for you. As said choose a fairly simple shaped part for starters. Plastic trim parts/covers etc or even house hold items such as bowls, trays etc. Dont choose something too small as small parts can often be more tricky to lay up than larger parts. You can make it a split mould even if it's not needed as practice for more awkward parts further down the line.