As a strategy should one always attack what they would consider easy?
Nope, it will all depend on the way your clan does war. Remember that a clan war is an event where all the clan members work together to achieve victory. As such, it is usually most appropriate to get to a consensus and everyone attacks their designated target and try to get 3 stars on them.
For instance, it is close to impossible for a TH9 to get 3 stars on a well developed TH10. As such, during the first hours of the war, it would not be likely that the clan would ask a TH9 player to attack a TH10 player. However, if the war is coming to a close, all TH9 on the opposite side and below have been 3 starred, the score is currently a draw, your clan desperately need at least one star to win, and the last player with an attack left is this TH9 who has a possibility to get 1 or 2 stars on this TH10, so it would be likely that this player would go for it for the benefit of the clan.
Should it be attack ones you are 100% sure you can get all 3 stars or attack ones you are fairly confident you can get at least 1 star or attack ones you think you have a chance or winning and doubt others can do it?
You need to trust your other members. If you don't, there won't be teamwork. Coming again to the point I raised above, it should be the clan to decide what is your target (or you suggest and they agree or refuse it) so if they gave you something too difficult for you to 3 star, it would be unfair that they kick you. If they told you to attack a certain base but you went for a harder base, then it's only fair that you get a penalty.
If the clan never consults each other for their target base, then I don't think it's a proper clan but more like individualistic players. Consider a case where the number 1 on the opposite side has their town hall way outside the base. It would be easy to get 1 star on it, right? Now every one uses their first attack on this base, effectively getting only 1 star, lots of war bonus loot but then score only a few stars on their second attacks, ending up losing the war... well, their previously 'big war loot' now has become 30% of its original size...
There's no strategy defined for Clan Wars. Every clan can come up with their own and do what they find works best for them.
Some clans tell their players to attack the base directly opposite them for their first attack, and try to get 3 stars for their second attack on any base lower than theirs if there are, which I think works pretty well, especially if additionally, the order of doing the second attack should start from the bottom so that the weaker players try to get 3 stars first and if they cannot, slightly stronger players will try in turn so that in the end, the clan is maximizing the number of stars it gets.
By the way, do you get no loot if you participated in the clan war but didn't get any stars?
As answered by Ben in the comments, you need to score at least 1 star to win the war loot.
I apologize if it's tl;dr ^^;