Travel by Train
On arrival at Gare du Nord you need to head for Metro line 4 – purple in colour and take Metro direction Porte D’Orleans (General LeClerc) – the actual journey time between the Metro stations is estimated at 14 minutes.
The ticket machines at Gare Montparnasse can be a bit frustrating, if possible get all your tickets in advance (you can only collect Eurostar tickets from the self service machines at St Pancras station).
The Paris Metro is a pretty user friendly system – their website offers plenty of advice on getting around.
Check to see if you can take a train from Lille direct to Poitiers instead of travelling via Paris.
If you are catching a connecting train from Lille be aware that some trains go from Gare Lille Flandres as opposed to Gare Lille Europe which is where Eurostar services arrive. It is a short walk from Lille Europe to Lille Flandres stations.
If you are likely to travel regularly by train in France SNCF operate a range of discount cards that are worth considering.