In reply to Oujmik:
There are some great suggestions but (at the risk of seeming a spoilsport), might I suggest a note of caution?
Bad conditions (wet rock, high winds, sleet, etc) can make routes dramatically harder. Being cold, just 'cos it's cold and/or being on a route for ages can make stuff seem harder. Being knackered (from being on a route for ages?) can make stuff seem harder. Being scared can make stuff seem harder.
Compound these factors - cold, wet rock, knackered, scared and maybe add in impending darkness and... can you see where this is heading? OK, that's your worst case scenario and a nice, dry sunny day when everything goes right is your best scenario. But you need to work from your worst scenario, not assume everything going right.
Your technical standard (Mod/Diff) doesn't allow anything up your sleeve if something goes wrong. What if you just get off-route and end up on a greasy polished Severe?
I'd stick to the easy routes on Tryfan Bach, for now. They're great. Although they're by the road, you feel in the mountains. Take as much time as you need but see how much time you take. How easy is it to find belays? How long does it take? What about your mates' skills/standards? Could they take over on a long route if you were injured?
Doing those easy routes will give you great experience. Do 'em again, if need be - but get experience under your belt. Then get a guide (say someone like Andy Newton in Llanberis) for a day or two. See what he thinks of your expertise. Do more challenging routes with him.
I'll not carry on. It's a never-ending process of learning. But what none of us wants to be is an accident statistic. And, sadly, Ogwen sees lots of accident statistics. Don't be one.
Mick