The Hammers have struggled since an opening-day victory over Cardiff, scoring just twice in a four-game winless streak.
| GOAL PREDICTS
|5/1||Jermain Defoe is 5/1 with BetVictor to score two or more goals v West Ham
"They are still a very objective and aggressive team. They are very direct and we know what to expect against them," is quoted as saying by Sky Sports.
"We will have to be alert at set plays, crosses into the box and make the play very, very strong.
"We were successful against them last season, winning home and away, and we are highly motivated for the game against West Ham.
"A London derby is always difficult, so it will be an extremely difficult match."
While Sam Allardyce is struggling to find goals in his side, Jermain Defoe notched his seventh of the season against Anzhi Makhachkala on Thursday.
Villas-Boas, though, still feels his tactical approach suits a lone frontman - with Roberto Soldado first choice - but he has opened the door for Defoe and Emmanuel Adebayor to challenge for a first-team berth.
"At the moment we have found extreme comfort in playing one striker rather than two like last season," he added.
"What Ade will give us is that possibility, that link-up play he does so well with somebody else.
"At the moment we continue to play with one striker. We scored so many goals and we don't suffer, so it looks like the way forward for us. All three of them will be in competition for that place."